A golf ball comprising a very-low melt flow inner cover layer composition

ABSTRACT

A golf ball including a core; an inner cover layer formed from a first thermoplastic composition and having a thickness of about 0.005 inches to 0.40 inches and a surface hardness of about 60 Shore D or greater; and an outer cover layer formed from a thermoplastic polyurethane material and having a thickness of about 0.01 inches to 0.075 inches and a surface hardness of about 60 Shore D or less. The thermoplastic composition has a first melt flow index at 280° C. under a 10-kg load of less than about 35 g/10 min and a second melt flow index at 265° C. under a 5-kg load of less than about 10 g/10 min.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/936,500, filed Mar. 27, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/799,849, filed Jul. 15, 2015, now U.S. Pat. No.9,925,417, which is a continuation of U.S. patent application Ser. No.13/633,180, filed Oct. 2, 2012, now U.S. Pat. No. 9,084,916, which is acontinuation-in-part of U.S. patent application Ser. No. 12/469,381,filed May 20, 2009, now U.S. Pat. No. 8,337,331, the entire disclosuresof which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to golf balls, and moreparticularly to golf balls having multi-layer covers comprising athermoplastic inner cover layer, and a thermoset outer core layer.

BACKGROUND OF THE INVENTION

Golf balls having multi-cover layers are known as is the use of ionomersand highly neutralized polymers as cover layers. Several patents andpublished applications in the prior art teach that it is essential forcover materials to have good flow properties, in particular they shouldhave a high melt flow rate as demonstrated by having a high Melt FlowIndex (MFI). For example, U.S. Pat. No. 7,572,195 to Egashira et al.,U.S. Pub. Appl. No. 2010/0167841 to Okabe et al., and U.S. PatentApplication Serial No. 2010/0190580 to Higuchi et al. all teachcompositions for use as golf ball inner cover layers that have MFI's ofgreater than 2. Other references such as U.S. Patent Application SerialNos. 2010/0069173 to Okabe et al. and 2010/0075777 to Shigemitsu et al.teach compositions for use as golf ball inner cover layers that areblends of low MFI materials and high MFI materials. Other referencesteach a broad range of MFI, such as U.S. Patent Application Serial No.2011/0092312 to Shigemitsu, but only measured at a relatively lowtemperature, 190° C., and are silent as to the need for the material tobe low melt flow at the higher temperatures at which inner cover leakagemay occur.

Generally, golf ball cover layers are formed from thermoplastic and/orthermoset compositions. The present invention, however, provides a novelmulti-cover layer golf ball construction wherein an inner covercomprises a very low melt flow thermoplastic, and an outer cover layercomprises a thermoset or thermoplastic composition. A problem withmolding a thermosetting composition requiring an elevated temperatureand/or pressure to cure, over a higher melt flow thermoplasticcomposition such as an ionomer, is that the ionomer tends to flow out or“leak” out through the thermosetting layer during overmolding—ingeneral, there exist tremendous difficulties in molding high-temperaturethermoset materials over any soft layer. The invention herein seeks toreduce or eliminate “leakage” by either 1) reducing the melt flow of theionomeric material or 2) otherwise increasing the heat resistance of theionomer by modifying either the ionomeric resin itself prior to moldingor via a post-mold treatment to the ionomeric golf ball layer.

Ionomeric materials have long been used as layers of golf balls, verycommonly as inner or outer cover layers. Ionomers have excellenttoughness, crack resistance, resilience, and a wide range of hardnessvalues and moduli, which make them ideally suited for these types oflayers. Methods have been developed to compression or injection moldionomers into golf ball layers-such methods involve heating thematerials to soften and melt them thereby promoting flow to form thedesired layers. Ionomers have relatively low vicat softening points(47-71° C.) and low melting temperatures (70-96° C.) which makes themreadily moldable but also gives them inherently low resistance to heatand very poor high-temperature properties. As such, the inventivethermoplastic inner cover layers attempt to make use of materials havingvery low flow at elevated temperatures and/or high resistance to heat.

Most ionomers suitable for conventional golf ball layers have a percentneutralization of from 19 wt % to 69 wt %. Higher levels ofneutralization have previously been unsuitable for use by manufacturersor disclosed in the prior art as being useful, without addition of highlevels of metal cation-fatty acid flow modifiers, due to the difficultyof molding more highly-neutralized ionomers (>70 wt % neutralization).Whereas the conventional low-neutralization (19-69 wt %) ionomers may beeasily injection molded at temperatures of about 300° F. (149° C.) to450° (232° C.), the highly-neutralized and/or treated ionomers of theinvention must be molded at elevated temperatures of from about 500° F.(260° C.) to 680° F. (360° C.) and, more preferably, about 550° F. (288°C.) to 650° F. (343° C.), temperatures previously thought undesirable.When compression molding conventional ionomers (using a two-step processin which half shells are first injection molded, then placed around acore and compression molded into a ball) temperatures as low as 250° F.(121° C.) and typically from about 250° F. (121° C.) to 350° F.). (177°are used. The inventive ionomers must be processed at temps well above350° F. (177° C.).

The inventive constructions herein (i.e., thermoset or thermoplasticouter cover layers molded over a thermoplastic ionomeric layer)additionally involve the molding of a material requiring curing orprocessing at a temperature well above the softening and meltingtemperature of conventional ionomers. This presents a problem that theinvention herein seeks to solve, that is, provide ionomeric compositionsthat will not significantly soften and flow at the conditions that occurwhen overmolding with a material that requires elevated temperatures toform said overmolded layer.

Commercially ionomers are available in a wide range of melt flows, themelt flow being determined by the degree of neutralization of the acidmoiety of the acid copolymer with various metal cations, optimized forphysical properties such as toughness and elongation while maintainingmelt-processability. Neutralization to 90% and higher is known but isnot considered a commercially-viable and usable product because of theloss of melt-processability (producing a low melt flow or intractablematerial), particularly for copolymers with high acid levels. Forexample, U.S. Pat. No. 6,777,472 generally describes a process formodification of highly-neutralized ionomers by the addition of asufficient amount of specific organic fatty acids (or metal saltsthereof) in order to maintain melt-processability—unmodified,highly-neutralized ionomers are typically considered unworkablematerials because of their low-melt-flow properties.

Various methods of covalent crosslinking the outermost cover of golfballs are known. For example, U.S. Pat. No. 5,891,973 generallydiscloses an ionomer-covered golf ball that is irradiated via electronbeam exposure to increase the resistance to scuff and cut resistancewhen impacted with a golf club. Covalent crosslinking of non-ionomericgolf ball cover materials with the addition of peroxide is generallydisclosed in U.S. Pat. No. 6,303,704 which is also aimed at improvingthe scuff and cut resistance of softer covers. Ionomer outermost covers,particularly low modulus ionomers are susceptible to softening whenexposed to elevated temperatures, thereby losing dimple definition andnegatively impacting aerodynamic properties of the ball. One method toovercome this drawback is the irradiation via electron beam or exposureof the dimpled golf ball to gamma radiation, which is generallydisclosed in U.S. Pat. No. 6,350,793. None of these references, however,disclose using novel low-melt-flow (or altered, temperature resistant)thermoplastics as a core layer sandwiched between two, thermosettingrubber core layers.

There remains a need, therefore, for low melt flow and/or hightemperature resistant thermoplastic ionomeric materials for use in thenovel multi-layer golf ball covers herein. The use of these compositionssignificantly reduces or eliminates the “leakage” of the ionomeric layerinto or through the outer core layer, thereby giving a ball havingimproved consistency of properties as well as improved durability andmuch reduced susceptibility to breakage when struck with a club head.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball having a core, an innercover layer, and an outer cover layer. The inner cover layer is formedfrom a thermoplastic composition and has a thickness of about 0.005 to0.40 inches and a surface hardness of about 60 Shore D or greater. Theouter cover layer is formed from a thermoset material and has athickness of about 0.01 to 0.05 inches and a surface hardness of about60 Shore D or less. The thermoplastic composition has a first melt flowindex at 280° C. under a 10-kg load of less than about 35 g/10 min and asecond melt flow index at 265° C. under a 5-kg load of less than about10 g/10 min.

The first melt flow index is about 20 g/10 min or less, preferably about10 g/10 min or less. The second melt flow index is about 5 g/10 min orless. In another embodiment, the thermoplastic composition has a thirdmelt flow index at 190° C. under a 2.16-kg load of less than about 2g/10 min, more preferably less than about 1 g/10 min. The thermoplasticcomposition may include an ionomer. The ionomer is typically neutralizedby a metal cation to 70 wt. % or greater, more preferably 80 wt. % orgreater, most preferably 90 wt. % or greater. The thermoplasticcomposition may include an amine or a peroxide compound, be treated withradiation, or include an ionomer and a higher-melting-temperaturethermoplastic resin. The thermoplastic composition may alternativelyinclude an ionomer and a reactive polymer. The core may also be a ‘dualcore’, including an inner core and an outer core layer.

The present invention is also directed to a golf ball formed from acore, an inner cover, and an outer cover. The inner cover layer may beformed from a first thermoplastic composition and has a thickness ofabout 0.005 to 0.10 inches and a surface hardness of about 60 Shore D orgreater. The outer cover layer is formed from a second thermoplasticcomposition, in a particular embodiment, thermoplastic polyurethane, andhas a thickness of about 0.01 to 0.05 inches and a surface hardness ofabout 60 Shore D or less. The first thermoplastic composition preferablyhas a first melt flow index at 280° C. under a 10-kg load of less thanabout 35 g/10 min and a second melt flow index at 265° C. under a 5-kgload of less than about 10 g/10 min. In a preferred embodiment, thefirst and second melt flow indices are less than the melt flow index ofthe second thermoplastic composition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention may be more fullyunderstood with reference to, but not limited by, the followingdrawings:

FIG. 1 is a representative cross-section of a golf ball of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

A golf ball having a core and a multi-layer cover enclosing the core isdisclosed. The core generally comprises a thermosetting rubber single ormultiple layer core, and may further comprise a thermoplastic inner,intermediate, or outer core layer. The inner, intermediate, and/or outercore layers may be formed of more than one layer. The multi-layer corehas an overall outer diameter within a range having a lower limit of1.000 or 1.300 or 1.400 or 1.500 or 1.600 or 1.610 inches and an upperlimit of 1.620 or 1.630 or 1.640 inches. In a particular embodiment, thesingle or multi-layer core has an overall outer diameter of 1.500 inchesor 1.510 inches or 1.530 inches or 1.550 inches or 1.570 inches or 1.580inches or 1.590 inches or 1.600 inches or 1.610 inches or 1.620 inches.

In one preferred embodiment, the core consists of a single layer formedfrom a thermoset rubber composition. In another embodiment, the centerand/or outer core layer consists of two layers, each of which is formedfrom the same or different thermoset rubber compositions.

Suitable rubber compositions for forming the core layer comprise a baserubber, an initiator agent, a co-agent, and optionally one or more of azinc oxide, zinc stearate or stearic acid, antioxidant, and asoft-and-fast agent. Suitable base rubbers include natural and syntheticrubbers including, but not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), styrene-butadiene rubber, styrenicblock copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, andthe like, where “S” is styrene, “I” is isobutylene, and “B” isbutadiene), butyl rubber, halobutyl rubber, polystyrene elastomers,polyethylene elastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and combinations of two ormore thereof. Diene rubbers are preferred, particularly polybutadiene,styrene-butadiene, and mixtures of polybutadiene with other elastomerswherein the amount of polybutadiene present is at least 40 wt % based onthe total polymeric weight of the mixture. Particularly preferredpolybutadienes include high-cis neodymium-catalyzed polybutadienes andcobalt-, nickel-, or lithium-catalyzed polybutadienes. Suitable examplesof commercially-available polybutadienes include, but are not limitedto, BUNA CB high-cis neodymium-catalyzed polybutadiene rubbers, such asBUNA CB 23, and TAKTENE high-cis cobalt-catalyzed polybutadiene rubbers,such as TAKTENE 220 and 221 from Lanxess Corp.; SE BR-1220 from DowChemical Company; EUROPRENE NEOCIS BR 40 and BR 60 from Polimeri Europa;UBEPOL-BR rubbers from UBE Industries, Inc.; BR 01 from Japan SyntheticRubber Co., Ltd.; and NEODENE high-cis neodymium-catalyzed polybutadienerubbers, such as NEODENE BR 40 from Karbochem.

Suitable initiator agents include organic peroxides, high energyradiation sources capable of generating free radicals, and combinationsthereof. High energy radiation sources capable of generating freeradicals include, but are not limited to, electron beams, ultra-violetradiation, gamma radiation, X-ray radiation, infrared radiation, heat,and combinations thereof.

Suitable organic peroxides include, but are not limited to, dicumylperoxide; n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; lauryl peroxide; benzoyl peroxide; andcombinations thereof. Examples of suitable commercially-availableperoxides include, but are not limited to PERKADOX BC dicumyl peroxidefrom Akzo Nobel, and VAROX peroxides, such as VAROX ANS benzoyl peroxideand VAROX 231 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane from RTVanderbilt Company, Inc. Peroxide initiator agents are generally presentin the rubber composition in an amount of at least 0.05 parts by weightper 100 parts of the base rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 0.8 parts or 1 part or 1.25parts or 1.5 parts by weight per 100 parts of the base rubber, and anupper limit of 2.5 parts or 3 parts or 5 parts or 6 parts or 10 parts or15 parts by weight per 100 parts of the base rubber.

Co-agents are commonly used with peroxides to increase the state ofcure. Suitable coagents include, but are not limited to, metal salts ofunsaturated carboxylic acids; unsaturated vinyl compounds andpolyfunctional monomers (e.g., trimethylolpropane trimethacrylate);phenylene bismaleimide; and combinations thereof. Particular examples ofsuitable metal salts include, but are not limited to, one or more metalsalts of acrylates, diacrylates, methacrylates, and dimethacrylates,wherein the metal is selected from magnesium, calcium, zinc, aluminum,lithium, nickel, and sodium. In a particular embodiment, the co-agent isselected from zinc salts of acrylates, diacrylates, methacrylates,dimethacrylates, and mixtures thereof. In another particular embodiment,the coagent is zinc diacrylate. When the co-agent is zinc diacrylateand/or zinc dimethacrylate, the co-agent is typically included in therubber composition in an amount within the range having a lower limit of1 or 5 or 10 or 15 or 19 or 20 parts by weight per 100 parts of the baserubber, and an upper limit of 24 or 25 or 30 or 35 or 40 or 45 or 50 or60 parts by weight per 100 parts of the base rubber. When one or moreless active co-agents are used, such as zinc monomethacrylate andvarious liquid acrylates and methacrylates, the amount of less activecoagent used may be the same as or higher than for zinc diacrylate andzinc dimethacrylate co-agents. The desired compression may be obtainedby adjusting the amount of crosslinking, which can be achieved, forexample, by altering the type and amount of co-agent.

The rubber composition optionally includes a curing agent. Suitablecuring agents include, but are not limited to, sulfur; N-oxydiethylene2-benzothiazole sulfenamide; N,N-di-ortho-tolylguanidine; bismuthdimethyldithiocarbamate; N-cyclohexyl 2-benzothiazole sulfenamide;N,N-diphenylguanidine; 4-morpholinyl-2-benzothiazole disulfide;dipentamethylenethiuram hexasulfide; thiuram disulfides;mercaptobenzothiazoles; sulfenamides; dithiocarbamates; thiuramsulfides; guanidines; thioureas; xanthates; dithiophosphates;aldehyde-amines; dibenzothiazyl disulfide; tetraethylthiuram disulfide;tetrabutylthiuram disulfide; and combinations thereof.

The rubber composition optionally contains one or more antioxidants.Antioxidants are compounds that can inhibit or prevent the oxidativedegradation of the rubber. Some antioxidants also act as free radicalscavengers; thus, when antioxidants are included in the rubbercomposition, the amount of initiator agent used may be as high or higherthan the amounts disclosed herein. Suitable antioxidants include, forexample, dihydroquinoline antioxidants, amine type antioxidants, andphenolic type antioxidants.

The rubber composition may contain one or more fillers to adjust thedensity and/or specific gravity of the core. Exemplary fillers includeprecipitated hydrated silica, clay, talc, asbestos, glass fibers, aramidfibers, mica, calcium metasilicate, zinc sulfate, barium sulfate, zincsulfide, lithopone, silicates, silicon carbide, diatomaceous earth,polyvinyl chloride, carbonates (e.g., calcium carbonate, zinc carbonate,barium carbonate, and magnesium carbonate), metals (e.g., titanium,tungsten, aluminum, bismuth, nickel, molybdenum, iron, lead, copper,boron, cobalt, beryllium, zinc, and tin), metal alloys (e.g., steel,brass, bronze, boron carbide whiskers, and tungsten carbide whiskers),oxides (e.g., zinc oxide, tin oxide, iron oxide, calcium oxide, aluminumoxide, titanium dioxide, magnesium oxide, and zirconium oxide),particulate carbonaceous materials (e.g., graphite, carbon black, cottonflock, natural bitumen, cellulose flock, and leather fiber),microballoons (e.g., glass and ceramic), fly ash, regrind (i.e., corematerial that is ground and recycled), nanofillers and combinationsthereof. The amount of particulate material(s) present in the rubbercomposition is typically within a range having a lower limit of 5 partsor 10 parts by weight per 100 parts of the base rubber, and an upperlimit of 30 parts or 50 parts or 100 parts by weight per 100 parts ofthe base rubber. Filler materials may be dual-functional fillers, suchas zinc oxide (which may be used as a filler/acid scavenger) andtitanium dioxide (which may be used as a filler/brightener material).

The rubber composition may also contain one or more additives selectedfrom processing aids, processing oils, plasticizers, coloring agents,fluorescent agents, chemical blowing and foaming agents, defoamingagents, stabilizers, softening agents, impact modifiers, free radicalscavengers, accelerators, scorch retarders, and the like. The amount ofadditive(s) typically present in the rubber composition is typicallywithin a range having a lower limit of 0 parts by weight per 100 partsof the base rubber, and an upper limit of 20 parts or 50 parts or 100parts or 150 parts by weight per 100 parts of the base rubber.

The rubber composition optionally includes a soft-and-fast agent.Preferably, the rubber composition contains from 0.05 phr to 10.0 phr ofa soft-and-fast agent. In one embodiment, the soft-and-fast agent ispresent in an amount within a range having a lower limit of 0.05 or 0.1or 0.2 or 0.5 phr and an upper limit of 1.0 or 2.0 or 3.0 or 5.0 phr. Inanother embodiment, the soft-and-fast agent is present in an amount offrom 2.0 phr to 5.0 phr, or from 2.35 phr to 4.0 phr, or from 2.35 phrto 3.0 phr. In an alternative high concentration embodiment, thesoft-and-fast agent is present in an amount of from 5.0 phr to 10.0 phr,or from 6.0 phr to 9.0 phr, or from 7.0 phr to 8.0 phr. In anotherembodiment, the soft-and-fast agent is present in an amount of 2.6 phr.

Suitable soft-and-fast agents include, but are not limited to,organosulfur and metal-containing organosulfur compounds; organic sulfurcompounds, including mono, di, and polysulfides, thiol, and mercaptocompounds; inorganic sulfide compounds; blends of an organosulfurcompound and an inorganic sulfide compound; Group VIA compounds;substituted and unsubstituted aromatic organic compounds that do notcontain sulfur or metal; aromatic organometallic compounds;hydroquinones; benzoquinones; quinhydrones; catechols; resorcinols; andcombinations thereof.

As used herein, “organosulfur compound” refers to any compoundcontaining carbon, hydrogen, and sulfur, where the sulfur is directlybonded to at least 1 carbon. As used herein, the term “sulfur compound”means a compound that is elemental sulfur, polymeric sulfur, or acombination thereof. It should be further understood that the term“elemental sulfur” refers to the ring structure of S₈ and that“polymeric sulfur” is a structure including at least one additionalsulfur relative to elemental sulfur.

Particularly suitable as soft-and-fast agents are organosulfur compoundshaving the following general formula:

where R₁-R₅ can be C₁₋₈ alkyl groups; halogen groups; thiol groups(—SH), carboxylated groups; sulfonated groups; and hydrogen; in anyorder; and also pentafluorothiophenol; 2-fluorothiophenol;3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol;2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol;2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol;4-chlorotetrafluorothiophenol; pentachlorothiophenol;2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol;2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol;3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol;2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol;pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol;4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol;3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol;3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol;2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol;3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol;2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol;2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol;2,3,5,6-tetraiodothiophenoland; zinc salts thereof; non-metal saltsthereof, for example, ammonium salt of pentachlorothiophenol; magnesiumpentachlorothiophenol; cobalt pentachlorothiophenol; and combinationsthereof. Preferably, the halogenated thiophenol compound ispentachlorothiophenol, which is commercially available in neat form orunder the tradename STRUKTOL, a clay-based carrier containing the sulfurcompound pentachlorothiophenol loaded at 45 percent (correlating to 2.4parts PCTP). STRUKTOL is commercially available from Struktol Company ofAmerica of Stow, Ohio. PCTP is commercially available in neat form andin the salt form from eChinachem of San Francisco, Calif. Mostpreferably, the halogenated thiophenol compound is the zinc salt ofpentachlorothiophenol.

Suitable metal-containing organosulfur compounds include, but are notlimited to, cadmium, copper, lead, and tellurium analogs ofdiethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, and combinations thereof.

Suitable disulfides include, but are not limited to, 4,4′-diphenyldisulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyl disulfide;bis(2-aminophenyl) disulfide; bis(4-aminophenyl) disulfide;bis(3-aminophenyl) disulfide; 2,2′-bis(4-aminonaphthyl) disulfide;2,2′-bis(3-aminonaphthyl) disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(5-aminonaphthyl) disulfide;2,2′-bis(6-aminonaphthyl) disulfide; 2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl) disulfide;1,1′-bis(2-aminonaphthyl) disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl) disulfide;1,1′-bis(4-aminonaphthyl) disulfide; 1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl) disulfide;1,1′-bis(7-aminonaphthyl) disulfide; 1,1′-bis(8-aminonaphthyl)disulfide; 1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl) disulfide;bis(2-chlorophenyl) disulfide; bis(3-chlorophenyl) disulfide;bis(4-bromophenyl) disulfide; bis(2-bromophenyl) disulfide;bis(3-bromophenyl) disulfide; bis(4-fluorophenyl) disulfide;bis(4-iodophenyl) disulfide; bis(2,5-dichlorophenyl) disulfide;bis(3,5-dichlorophenyl) disulfide; bis(2,4-dichlorophenyl) disulfide;bis(2,6-dichlorophenyl) disulfide; bis(2,5-dibromophenyl) disulfide;bis(3,5-dibromophenyl) disulfide; bis(2-chloro-5-bromophenyl) disulfide;bis(2,4,6-trichlorophenyl) disulfide; bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl) disulfide; bis(2-cyanophenyl) disulfide;bis(4-nitrophenyl) disulfide; bis(2-nitrophenyl) disulfide;2,2′-dithiobenzoic acid ethylester; 2,2′-dithiobenzoic acid methylester;2,2′-dithiobenzoic acid; 4,4′-dithiobenzoic acid ethylester;bis(4-acetylphenyl) disulfide; bis(2-acetylphenyl) disulfide;bis(4-formylphenyl) disulfide; bis(4-carbamoylphenyl) disulfide;1,1′-dinaphthyl disulfide; 2,2′-dinaphthyl disulfide; 1,2′-dinaphthyldisulfide; 2,2′-bis(1-chlorodinaphthyl) disulfide;2,2′-bis(1-bromonaphthyl) disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphthyl) disulfide;2,2′-bis(1-acetylnaphthyl) disulfide; and the like; and combinationsthereof.

Suitable inorganic sulfide compounds include, but are not limited to,titanium sulfide, manganese sulfide, and sulfide analogs of iron,calcium, cobalt, molybdenum, tungsten, copper, selenium, yttrium, zinc,tin, and bismuth.

Suitable Group VIA compounds include, but are not limited to, elementalsulfur and polymeric sulfur, such as those from Elastochem, Inc. ofChardon, Ohio; sulfur catalyst compounds which include PB(RM-S)-80elemental sulfur and PB(CRST)-65 polymeric sulfur, each of which isavailable from Elastochem, Inc; tellurium catalysts, such as TELLOY, andselenium catalysts, such as VANDEX, from RT Vanderbilt Company, Inc.

Suitable substituted and unsubstituted aromatic organic components thatdo not include sulfur or a metal include, but are not limited to,4,4′-diphenyl acetylene, azobenzene, and combinations thereof. Thearomatic organic group preferably ranges in size from C₆₋₂₀, morepreferably from C₆₋₁₀.

Suitable substituted and unsubstituted aromatic organometallic compoundsinclude, but are not limited to, those having the formula(R₁)_(x)—R₃-M-R₄—R₂)_(y), wherein R₁ and R₂ are each hydrogen or asubstituted or unsubstituted C₁₋₂₀ linear, branched, or cyclic alkyl,alkoxy, or alkylthio group, or a single, multiple, or fused ring C₆₋₂₄aromatic group; x and y are each an integer from 0 to 5; R₃ and R₄ areeach selected from a single, multiple, or fused ring C₆₋₂₄ aromaticgroup; and M includes an azo group or a metal component. Preferably, R₃and R₄ are each selected from a C₆₋₁₀ aromatic group, more preferablyselected from phenyl, benzyl, naphthyl, benzamido, and benzothiazyl.Preferably R₁ and R₂ are each selected from substituted andunsubstituted C₁₋₁₀ linear, branched, and cyclic alkyl, alkoxy, andalkylthio groups, and C₆₋₁₀ aromatic groups. When R₁, R₂, R₃, and R₄ aresubstituted, the substitution may include one or more of the followingsubstituent groups: hydroxy and metal salts thereof; mercapto and metalsalts thereof; halogen; amino, nitro, cyano, and amido; carboxylincluding esters, acids, and metal salts thereof; silyl; acrylates andmetal salts thereof; sulfonyl and sulfonamide; and phosphates andphosphites. When M is a metal component, it may be any suitableelemental metal. The metal is generally a transition metal, and ispreferably tellurium or selenium.

Suitable hydroquinones include, but are not limited to, compoundsrepresented by the following formula, and hydrates thereof:

where each of R₁, R₂, R₃, and R₄ is independently selected fromhydrogen, a halogen group (F, Cl, Br, I), an alkyl group, a carboxylgroup (—COOH) and metal salts thereof (e.g., —COO⁻M⁺) and esters thereof(—COOR), an acetate group (—CH₂COOH) and esters thereof (—CH₂COOR), aformyl group (—CHO), an acyl group (—COR), an acetyl group (—COCH₃), ahalogenated carbonyl group (—COX), a sulfo group (—SO₃H) and estersthereof (—SO₃R), a halogenated sulfonyl group (—SO₂X), a sulfino group(—SO₂H), an alkylsulfinyl group (—SOR), a carbamoyl group (—CONH₂), ahalogenated alkyl group, a cyano group (—CN), an alkoxy group (—OR), ahydroxy group (—OH) and metal salts thereof (e.g., —O⁻M⁺), an aminogroup (—NH₂), a nitro group (—NO₂), an aryl group (e.g., phenyl, tolyl,etc.), an aryloxy group (e.g., phenoxy, etc.), an arylalkyl group (e.g.,cumyl (—C(CH₃)₂—C₆H₆) or benzyl (—CH₂—C₆H₆)), a nitroso group (—NO), anacetamido group (—NHCOCH₃), and a vinyl group (—CH═CH₂). Particularlypreferred hydroquinones include compounds represented by the aboveformula, and hydrates thereof, wherein each of R₁, R₂, R₃, and R₄ isindependently selected from the group consisting of: a metal salt of acarboxyl group (e.g., —COO⁻M⁺), an acetate group (—CH₂COOH) and estersthereof (—CH₂COOR), a hydroxy group (—OH), a metal salt of a hydroxygroup (e.g., —O⁻M⁺), an amino group (—NH₂), a nitro group (—NO₂), anaryl group (e.g., phenyl, tolyl, etc.), an aryloxy group (e.g., phenoxy,etc.), an arylalkyl group (e.g., cumyl (—C(CH₃)₂—C₆H₆) or benzyl(—CH₂—C₆H₆)), a nitroso group (—NO), an acetamido group (—NHCOCH₃), anda vinyl group (—CH═CH₂). Examples of particularly suitable hydroquinonesinclude, but are not limited to, hydroquionone; tetrachlorohydroquinone;2-chlorohydroquionone; 2-bromohydroquinone; 2,5-dichlorohydroquinone;2,5-dibromohydroquinone; tetrabromohydroquinone; 2-methylhydroquinone;2-t-butylhydroquinone; 2,5-di-t-amylhydroquinone; and2-(2-chlorophenyl)hydroquinone hydrate. Hydroquinone andtetrachlorohydroquinone are particularly preferred, and even moreparticularly preferred is 2-(2-chlorophenyl)hydroquinone hydrate.

Suitable benzoquinones include, but are not limited to, compoundsrepresented by the following formula, and hydrates thereof:

where each of R₁, R₂, R₃, and R₄ is independently selected from theligands disclosed above for the hydroquinones. Particularly preferredbenzoquinones include compounds represented by the above formula, andhydrates thereof, where each of R₁, R₂, R₃, and R₄ is independentlyselected from the group consisting of: a metal salt of a carboxyl group(e.g., —COO⁻M⁺), an acetate group (—CH₂COOH) and esters thereof(—CH₂COOR), a hydroxy group (—OH), a metal salt of a hydroxy group(e.g., —O⁻M⁺), an amino group (—NH₂), a nitro group (—NO₂), an arylgroup (e.g., phenyl, tolyl, etc.), an aryloxy group (e.g., phenoxy,etc.), an arylalkyl group (e.g., cumyl (—C(CH₃)₂—C₆H₆) or benzyl(—CH₂—C₆H₆)), a nitroso group (—NO), an acetamido group (—NHCOCH₃), anda vinyl group (—CH═CH₂). Methyl p-benzoquinone and tetrachlorop-benzoquinone are more particularly preferred.

Suitable quinhydrones include, but are not limited to, compoundsrepresented by the following formula, and hydrates thereof:

where each of R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ is independentlyselected from the ligands disclosed above for the hydroquinones andbenzoquinones. Particularly preferred quinhydrones include compoundsrepresented by the above formula, and hydrates thereof, wherein each ofR₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ is independently selected from ametal salt of a carboxyl group (e.g., —COO⁻M⁺), an acetate group(—CH₂COOH) and esters thereof (—CH₂COOR), a hydroxy group (—OH), a metalsalt of a hydroxy group (e.g., —O⁻M⁺), an amino group (—NH₂), a nitrogroup (—NO₂), an aryl group (e.g., phenyl, tolyl, etc.), an aryloxygroup (e.g., phenoxy, etc.), an arylalkyl group (e.g., cumyl(—C(CH₃)₂—C₆H₆) or benzyl (—CH₂—C₆H₆)), a nitroso group (—NO), anacetamido group (—NHCOCH₃), and a vinyl group (—CH═CH₂). Particularlypreferred quinhydrones also include compounds represented by the aboveformula wherein each of R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ is hydrogen.

Suitable catechols include, but are not limited to, compoundsrepresented by the following formula, and hydrates thereof:

where each of R₁, R₂, R₃, and R₄, is independently selected from theligands disclosed above for the hydroquinones, benzoquinones, andquinhydrones.

Suitable resorcinols include, but are not limited to, compoundsrepresented by the following formula, and hydrates thereof:

where each of R₁, R₂, R₃, and R₄ is independently selected from theligands disclosed above for the hydroquinones, benzoquinones,quinhydrones, and catechols. 2-Nitroresorcinol is particularlypreferred.

When the rubber composition includes one or more hydroquinones,benzoquinones, quinhydrones, catechols, resorcinols, or a combinationthereof, the total amount of hydroquinone(s), benzoquinone(s),quinhydrone(s), catechol(s), and/or resorcinol(s) present in thecomposition is typically at least 0.1 parts by weight or at least 0.15parts by weight or at least 0.2 parts by weight per 100 parts of thebase rubber, or an amount within the range having a lower limit of 0.1parts or 0.15 parts or 0.25 parts or 0.3 parts or 0.375 parts by weightper 100 parts of the base rubber, and an upper limit of 0.5 parts or 1part or 1.5 parts or 2 parts or 3 parts by weight per 100 parts of thebase rubber.

In a particularly preferred embodiment, the soft-and-fast agent isselected from zinc pentachlorothiophenol, pentachlorothiophenol, ditolyldisulfide, diphenyl disulfide, dixylyl disulfide, 2-nitroresorcinol, andcombinations thereof.

Referring to FIG. 1, in one embodiment of the present invention the golfball 10 includes a core 12, the materials of which are described above,an inner cover layer 14, and an outer cover layer 16.

The inner cover layers of the present invention are formed from athermoplastic ionomeric material that either 1) has a low melt flowindex and/or 2) has an improved heat resistance. Preferably, thethermoplastic, ionomeric compositions are used to form an inner coverlayer in a multi-layer cover

Improved heat resistance is important to this cover construction, asdescribed in detail in the background section, because the outer coverincludes a thermosetting or thermoplastic outer cove layer that must bemolded over the ionomeric inner cover layer. When using a conventionalionomeric composition, which has low heat resistance and relatively highmelt flow properties, flow-out or leakage of the ionomeric layer into(and possibly through) the overmolded thermoset or thermoplastic layerduring compression molding at an elevated temperature and pressure is aproblem.

In one embodiment, a reduced melt flow ionomer is made by neutralizingabout 70 wt. % or more, 75 wt. % or more, preferably 80 wt. % or more,more preferably at least 90 wt. %, and most preferably at least about 95wt. % of the acid groups without the use of any “ionic plasticizer” suchas the fatty acids or fatty acid salts required to form thehighly-neutralized polymers. In a preferred embodiment a high acidionomer containing 19 wt. % to 20 wt. % methacrylic or acrylic acid isneutralized with a blend of zinc and sodium cations to the 95 wt. %level such that the melt flow of the composition at 190° C. is very low(less than 0.5 g/10 min) and the melt flow at 280° C. is less than about0.50 g/10 min.

The melt flow indices of the thermoplastic, preferably ionomeric,polymers used to form the inner cover layers of the invention shouldhave a melt flow index, as measured at 280° C. under a mass of 10 kg, ofless than about 35 g/10 min, preferably less than about 20 g/10 min, andmost preferably less than about 10 g/10 min. In a preferred embodiment,these melt flow indices have concurrent melt flow indices, as measuredat 265° C. under a mass of 5 kg, of less than about 10 g/10 min,preferably less than about 5 g/10 min. In a preferred particularlyembodiment, both of these melt flow indices further have concurrent meltflow indices, as measured at 190° C. and 230° C. under a mass of 2.16kg, of less than about 2 g/10 min, preferably less than about 1 g/10min, more preferably less than about 0.5 g/10 min, and most preferablyless than about 0.1 g/10 min.

Other preferred cation sources include lithium, magnesium, manganese,aluminum, potassium, calcium, zirconium, barium, etc. When aluminum isused it is preferably used at low levels with another cation source,such as zinc, sodium, or lithium, since aluminum has a dramatic effecton melt flow reduction and often cannot be used alone at high levels.Very high surface area cation sources, such as micro and nano-scalecation sources, are particularly preferred.

Where processability of such highly-neutralized ionomers may become verydifficult, a small level of plasticizer may be tolerable withoutadversely affecting the heat resistance properties. For example, perhaps0.5 phr to 5 phr of a fatty acid, polyethylene glycol, wax,bis-stearamide, mineral, or phthalate, may be used.

In another embodiment, an amine or pyridine compound is used, preferablyin addition to a metal cation, to produce a reduced melt flow ionomer.Suitable examples include ethylamine, methylamine, diethylamine,tert-butylamine, dodecylamine, etc.

The addition of fillers, fibers, flakes is also believed to promote lowflow. Particularly preferred additives of this nature include, but arenot limited to, very-high-surface-area fillers that have an affinity forthe acid groups in ionomer. In particular, fillers, fibers or flakeshaving cationic nature such that they may also contribute to theneutralization of the ionomer are suitable. Aluminum oxide comprisingfillers are preferred. Also, silica, fumed silica, or precipitatedsilica, such as those sold under the tradename HISIL from PPGIndustries, or carbon black. Nano-scale materials are also preferred andinclude, but are not limited to, nanotubes, nanoflakes, nanofillers, ornanoclays.

In another embodiment, a peroxide or other source of free radicals isadded to the ionomer and is allowed to react (in an extruder or in aninjection molding machine, just prior to the golf ball layer beingmolded). The peroxide is added at a relatively low activity level ofabout 0.01 to 5.00 phr, more preferably about 0.025 to 2.50 phr, andmost preferably about 0.05 to 1.50 phr.

In another embodiment, a pre-molded layer of a golf ball comprising anionomeric composition is treated with radiation (i.e., such as e-beam,gamma, X-ray, UV, etc.) to effect crosslinking and thus increase theheat resistance of the layer. Additionally, post-molding treatment,involving dipping or soaking the ionomer layer in a solution of aneutralizing or crosslinking agent, may be employed to reduce flow ofthe surface of the layer upon exposure to heating while adding the outercore layer. For example, exposing the molded layer to a peroxidesolution followed by heating to crosslink the “skin” of the ionomerlayer, or soaking the molded layer in a solution of aluminumacetylacetonate or aluminum isopropoxide to neutralize the “skin” of theionomer layer, are suitable.

The low flow and/or improved heat resistance compositions herein may beused in any core and/or cover layer where a layer is molded over the lowflow composition in a manner that would cause conventional materials toflow or flow-through that layer upon heating. For example the low flowcomposition may be used in a center, intermediate, or outer core layer,or in a cover layer of a multilayer golf ball, wherein the low flowcomposition is overmolded with a material that requires processing atsuch a temperature at or above the flow or melt temperature of thesubstrate layer.

A preferred embodiment includes the inner cover layers disclosed herein.Another preferred embodiment is a thermoplastic inner cover layer overwhich is molded a crosslinked diene rubber composition requiring a curetemperature well above the melting point of the thermoplastic innercover layer material. Another preferred embodiment is an inner coverlayer of a multilayer golf ball wherein the outer cover layer comprisesa crosslinked diene rubber composition. An alternative embodiment is aninner cover layer of a multilayer golf ball where the outer cover layercomprises a thermoplastic polyurethane or polyurea that is processed atelevated temperatures. Typically such materials are either injectionmolded directly over the inner cover layer using a retractable pinmolding process or by first injection molding half shells of the TPUfollowed by compression molding the half shells over the inner layer(which has previously been molded over the core). It is the latterprocess of compression molding a high melt temperature material (i.e.,TPU) over the inner cover layer which is very difficult to performwithout the inner cover “leaking” out at the equator. Any combination ofneutralization and treatment or altering method disclosed herein mayalso be used.

In another embodiment a blend of ionomer and a higher temperaturemelting thermoplastic resin is employed. For example, a blend of ionomerwith polyamide, polyester, polyethylene and PE containing low levels of(meth)acrylic acid, HYTREL etc., will increase the temperatureresistance of the thermoplastic core layer. A preferred example is ablend of a zinc ionomer (copolymer or terpolymer type) with NYLON 11 orNYLON 12 (although NYLON 6 or NYLON 66 may also be used). Nylons withbetter moisture stability are preferred.

In another embodiment an organosilane is grafted onto the ionomerbackbone using a catalyst via extrusion producing a still mainlythermoplastic material which is then injection or compression moldedinto an inner cover layer. The bulk of the crosslinking is achievedlater by reacting this layer by exposing it to moisture where the watermolecules diffuse into the cover and react with the organosilane sidechains producing siloxane crosslinks which directly join together theionomer chains creating a crosslinked network that is more resistant toheat and pressure

Another embodiment is a blend of ionomer with a reactive polymer, suchas an epoxy resin or an epoxy-group functional polymer, such as glycidyl(meth)acrylate polymers disclosed in U.S. Pat. No. 4,968,752 toDuPont-Mitsui or U.S. Pat. Nos. 5,155,157 and 5,091,478. Also suitableare epoxy-acid-tert amines as disclosed in U.S. Pat. No. 6,087,417. AFUSABOND-type polymer containing very high levels of maleic anhydridemay also be suitable. Other examples include DuPont BEXLOY andREFLECTIONS polymers.

Other suitable thermoplastic compositions for use in the inner coverlayers include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof) havinggood inherent thermal stability (e.g., they melt at a high enoughtemperature) and used at levels so as to not cause detrimentalflow-through: (a) polyesters, particularly those modified with acompatibilizing group such as sulfonate or phosphonate, includingmodified poly(ethylene terephthalate), modified poly(butyleneterephthalate), modified poly(propylene terephthalate), modifiedpoly(trimethylene terephthalate), modified poly(ethylene naphthenate),and those disclosed in U.S. Pat. Nos. 6,353,050, 6,274,298, and6,001,930, the entire disclosures of which are hereby incorporatedherein by reference, and blends of two or more thereof; (b) polyamides,polyamide-ethers, and polyamide-esters, and those disclosed in U.S. Pat.Nos. 6,187,864, 6,001,930, and 5,981,654, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (c) polyurethanes, polyureas, polyurethane-polyureahybrids, and blends of two or more thereof; (d) fluoropolymers, such asthose disclosed in U.S. Pat. Nos. 5,691,066, 6,747,110 and 7,009,002,the entire disclosures of which are hereby incorporated herein byreference, and blends of two or more thereof; (e) polystyrenes, such aspoly(styrene-co-maleic anhydride), acrylonitrile-butadiene-styrene,poly(styrene sulfonate), polyethylene styrene, and blends of two or morethereof; (f) polyvinyl chlorides and grafted polyvinyl chlorides, andblends of two or more thereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

Other suitable thermoplastic compositions for use in the inner coverlayers include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof) treated bya radiation source (discussed above) and/or a peroxide (or otheraltering method described herein) so as to not cause detrimentalflow-through: (a) non-ionomeric acid polymers, such as E/Y- andE/X/Y-type copolymers, wherein E is an olefin (e.g., ethylene), Y is acarboxylic acid such as acrylic, methacrylic, crotonic, maleic, fumaric,or itaconic acid, and X is a softening comonomer such as vinyl esters ofaliphatic carboxylic acids wherein the acid has from 2 to 10 carbons,alkyl ethers wherein the alkyl group has from 1 to 10 carbons, and alkylalkylacrylates such as alkyl methacrylates wherein the alkyl group hasfrom 1 to 10 carbons; and blends of two or more thereof; (b)metallocene-catalyzed polymers, such as those disclosed in U.S. Pat.Nos. 6,274,669, 5,919,862, 5,981,654, and 5,703,166, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (c) polypropylenes and polyethylenes,particularly grafted polypropylene and grafted polyethylenes that aremodified with a functional group, such as maleic anhydride of sulfonate,and blends of two or more thereof; (d) polyvinyl acetates, preferablyhaving less than about 9% of vinyl acetate by weight, and blends of twoor more thereof; and (e) polyvinyl alcohols, and blends of two or morethereof.

Ionomeric compositions suitable for forming the inner cover layercomprise one or more acid polymers, each of which is partially- orhighly-neutralized (up to 100% and without the use of fatty acid/salts),and optionally additives, fillers, and/or melt flow modifiers. Suitableacid polymers are salts of homopolymers and copolymers ofα,β-ethylenically unsaturated mono- or di-carboxylic acids, andcombinations thereof, optionally including a softening monomer, andpreferably having an acid content (prior to neutralization) of from 1 wt% to 30 wt %, more preferably from 5 wt % to 20 wt %. The acid polymeris preferably neutralized to 70 wt % or higher, including up to 100 wt%, with a suitable cation source, such as metal cations and saltsthereof, organic amine compounds, ammonium, and combinations thereof.Preferred cation sources are metal cations and salts thereof, whereinthe metal is preferably lithium, sodium, potassium, magnesium, calcium,barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper,or a combination thereof.

Suitable additives and fillers include, for example, blowing and foamingagents, optical brighteners, coloring agents, fluorescent agents,whitening agents, UV absorbers, light stabilizers, defoaming agents,processing aids, mica, talc, nanofillers, antioxidants, stabilizers,softening agents, fragrance components, plasticizers, impact modifiers,acid copolymer wax, surfactants; inorganic fillers, such as zinc oxide,titanium dioxide, tin oxide, calcium oxide, magnesium oxide, bariumsulfate, zinc sulfate, calcium carbonate, zinc carbonate, bariumcarbonate, mica, talc, clay, silica, lead silicate, and the like; highspecific gravity metal powder fillers, such as tungsten powder,molybdenum powder, and the like; regrind, i.e., cover material that isground and recycled; and nano-fillers.

In a particular embodiment, the inner cover layer is formed from a blendof two or more ionomers. In a particular aspect of this embodiment, theintermediate core layer is formed from a 50/50 wt % blend of twodifferent highly-neutralized ethylene/methacrylic acid copolymers.

In another particular embodiment, the inner cover layer is formed from ablend of one or more ionomers and a maleic anhydride-graftednon-ionomeric polymer. In a particular aspect of this embodiment, thenon-ionomeric polymer is a metallocene-catalyzed polymer. In anotherparticular aspect of this embodiment, the inner cover layer is formedfrom a blend of a highly-neutralized ethylene/methacrylic acid copolymerand a maleic anhydride-grafted metallocene-catalyzed polyethylene.

In yet another particular embodiment, the inner cover layer is formedfrom a composition selected from the group consisting ofhighly-neutralized ionomers optionally blended with a maleicanhydride-grafted non-ionomeric polymer; polyester elastomers; polyamideelastomers; and combinations of two or more thereof.

The thermoplastic inner cover layer is optionally treated or admixedwith a thermoset diene composition to reduce or prevent flow uponovermolding. Optional treatments may also include the addition ofperoxide to the material prior to molding, or a post-molding treatmentwith, for example, a crosslinking solution, electron beam, gammaradiation, isocyanate or amine solution treatment, or the like. Suchtreatments may prevent the inner cover layer from melting and flowing or“leaking” out at the mold equator, as the thermoset outer cover layer ismolded thereon at a temperature necessary to crosslink the outer corelayer, which is typically from 280° F. (138° C.) to 360° F. (182° C.)for a period of about 5 to 30 minutes.

The following examples are representative of the novel inner cover layercompositions of the invention and are non-limiting in scope of whatmaterials are suitable. Table I below presents 14 compositions, thefirst 10 being representative of the invention and the final 4 beingcontrols.

TABLE I Cross- Final linking Neutral'zn Final e-beam Cross-linkingReagent Achieved Ionomer dose Base polymer Ratio Reagent Added* (Mole %)Type (Mrad) Low-flow Ex 1 SURLYN ® 9120^(a) 100 NaOH ~41 77 Na/Zn — Ex 2SURLYN ® 9120 100 NaOH ~51 87 Na/Zn — Ex 3 PRIMACOR ® 100 Li(OH)•H₂0 9086 Li — 5986^(b) Ex 4 PRIMACOR ® 100 Li(OH)•H₂0 98 95 Li — 5986 Ex 5PRIMACOR ® 100 Li(OH)•H₂0 105 100 Li — 5986 Ex 6 NUCREL ® 2906^(c) 100Zn diacetate•2H₂0 110 ~100 Zn — Treated Ex 7 SURLYN ® 8140^(d)/ 50/50 —0 37 Na/Zn 10 SURLYN ® 9120 Ex 8 SURLYN ® 8140/ 50/50 — 0 37 Na/Zn 20SURLYN ® 9120 Ex 9 SURLYN ® 8140/ 50/50 — 0 37 Na/Zn 30 SURLYN ® 9120 Ex10 SURLYN ® 9120 100 PERKADOX ® 0 36 Zn — BC Comparative CE1 SURLYN ®9120 100 NaOH ~23 59 Na/Zn — CE2 SURLYN ® 8140/ 50/50 — 0 37 Na/Zn —SURLYN ® 9120 CE3 SURLYN ® 8940^(e)/ 75/25 — 0 38 Na/Zn — SURLYN ®9910^(f) CE4 HPF 2000^(g) 100 — 0 ~100 Mg — *to achieve additional mole% neutralization as indicated ^(a)partially Zn-neutralized, 19 wt. %methacrylic acid-ethylene copolymeric ionomer from DuPont^(b)unneutralized, 20.5 wt % acrylic acid-ethylene copolymer from Dow^(c)unneutralized, 19 wt % methacrylic acid-ethylene copolymer fromDuPont ^(d)partially Na-neutralized, 19 wt % methacrylic acid-ethylenecopolymeric ionomer from DuPont ^(e)partially Na-neutralized, 15 wt %methacrylic acid-ethylene copolymeric ionomer from DuPont ^(f)partiallyZn-neutralized, 15 wt % methacrylic acid-ethylene copolymeric ionomerfrom DuPont ^(g)fully Mg-neutralized, ~40% fatty acid salt modified,acrylic acid-ethylene-n-butyl acrylate terpolymeric ionomer availablefrom DuPont ^(h)dicumyl peroxide available from Akzo Nobel

Examples 1-6 and CE1 were made by combining the base polymer and thecross-linking reagent in a twin-screw extruder at appropriate zonetemperatures, screw speed, and feed rates to achieve the final mole %neutralization indicated in TABLE I. It is well known that cross-linkingreagents can be added to the extruder directly as a powder, as a causticaqueous solution, or as a masterbatch on a suitable carrier polymer.Examples 7-9 were made by injection molding a dry-blend of SURLYN 8140and 9120 around a core, and then radiation treating as indicated. Themelt flow index was then measured by removing and grinding the layer.Example 10 was made by compounding 0.5 phr of Perkadox BC into SURLYN9120 and curing for 15 min at 350° F. prior to measuring melt flow.Comparative examples 2-3 were prepared by melt blending.

TABLE II Melt Flow Condition - Temp (° C.)/Mass (kg) 190/2.16 230/2.16265/5 280/10 (g/10 min) (g/10 min) (g/10 min) (g/10 min) Pass/FailLow-flow Ex 1 L 0.70 8.00 33.4 Pass Ex 2 L 0.34 3.76 19.5 Pass Ex 3 L0.46 9.7 44 Pass Ex 4 L L 2.9 18.0 Pass Ex 5 L L 0.90 5.49 Pass Ex 6 L0.39 3.83 14.35 Pass Treated Ex 7 L L 0.37 5.82 Pass Ex 8 L L L 0.12Pass Ex 9 L L L L Pass Ex 10 L 0.13 3.86 18.4 Pass Comparative CE1 0.251.64 18.16 ~79 Fail CE2 2.41 14.34  ~86 x Fail CE3 2.14 9.38 ~77 x FailCE4 1.28 11.17  ~61 x Fail x = unmeasurable (flow was too high to make ameaningful measurement) L = low flow (flow was so low that nomeasureable material was extruded)

The melt flow rate characterizes the resistance to flow of a moltenplastic material and was determined in accordance with ASTM StandardD1238-04C using a Tinius-Olsen Extrusion Plastometer. The quantity ofmelt flow is measured by placing the sample in a heated barrel where itis held for a certain time then forced through a die using a weightedpiston. The ASTM standard specifies the barrel and die dimensions andsuggests a number of temperature and weight conditions typically chosento give results between 0.15 and 50 g/10 min. Melt flow results arereported as grams of material extruded over a 10-minute time interval ata specified temperature and load.

TABLE II contains melt flow data for each of the examples andcomparative examples, as well pass/fail data indicating whether a rubberouter cover layer could be compression molded over a layer of eachmaterial in TABLE I without that layer leaking out into the rubber outercover layer. Most of the melt flow temperature and mass conditions inTABLE II can be found in the ASTM method that was used to generate thedata in the table. The 190° C./2.16 kg condition is an industry standardused to report the melt flow of ionomers. Conventional thought was thatan ionomer with a melt flow index, under these conditions, of less thanabout 0.5 would be unmoldable (not melt processible) for golf ballapplications. The ASTM method suggests that if a melt flow value belowabout 0.15 g/10 minutes is obtained, that a higher temperature and/ormass should be used and suggests alternative combinations. TABLE IIshows a progression of increasing temperature/mass combinations tobetter characterize the flow properties of each material. Generally,materials should be compared to each other under identical melt flowconditions. In some cases, however, information can be obtained bycomparing melt flow values under different conditions. For example, amaterial that has a melt flow of 3 g/10 minutes at 280° C./10 kg flowsless than a material that has the same melt flow at 190° C./2.16 kg. Themelt flow conditions that we selected were also useful in determininginjection molding conditions for each material and as a predictor ofovermolding success or failure—CE1-4 all have substantially-higher meltflow values at a given condition relative to the inventive examples andare, therefore, insufficient for the inventive cover layers. Theabsolute value of the melt flow at each condition can be used to predictthe suitability of a candidate material for golf ball constructionsdescribed herein.

Suitable compositions for forming the outer cover layer include therubber compositions disclosed above for forming the center layer(s). Theouter cover layer composition may be the same or a different rubbercomposition than the composition(s) used to form the center layer(s).

The outer cover layer may further comprise from 1 to 100 phr of astiffening agent. Suitable stiffening agents include, but are notlimited to, ionomers, acid copolymers and terpolymers, polyamides, andpolyesters. A transpolyisoprene (e.g., TP-301 transpolyisoprene fromKuraray) or transbutadiene rubber may also be added to increasestiffness to a cover layer and/or improve cold-forming properties, whichmay improve processability by making it easier to mold inner cover layerhalf-shells during the golf ball manufacturing process. When included ina cover layer composition, the stiffening agent is preferably present inan amount of from 5 to 10 pph.

In one embodiment, the specific gravity of one or more of the coverlayers is increased. Suitable fillers for increasing specific gravityinclude, but are not limited to, metal and metal alloy powders,including, but not limited to, bismuth powder, boron powder, brasspowder, bronze powder, cobalt powder, copper powder, nickel-chromiumiron metal powder, iron metal powder, molybdenum powder, nickel powder,stainless steel powder, titanium metal powder zirconium oxide powder,tungsten metal powder, beryllium metal powder, zinc metal powder, andtin metal powder; metal flakes, including, but not limited to, aluminumflakes; metal oxides, including, but not limited to, zinc oxide, ironoxide, aluminum oxide, titanium dioxide, magnesium oxide, zirconiumoxide, and tungsten trioxide; metal stearates; particulate carbonaceousmaterials including, but not limited to, graphite and carbon black; andnanoparticulates and hybrid organic/inorganic materials. Particularlysuitable density-increasing fillers include, but are not limited to,tungsten, tungsten oxide, tungsten metal powder, zinc oxide, bariumsulfate, and titanium dioxide.

In another embodiment, the specific gravity of one or more of the coverlayers is reduced. The specific gravity of a layer can be reduced byincorporating cellular resins, low specific gravity fillers, fibers,flakes, or spheres, or hollow microspheres or balloons, such as glassbubbles or ceramic zeospheres, in the polymeric matrix. The specificgravity of a layer can also be reduced by foaming. Typical physicalfoaming/blowing agents include volatile liquids such as freons, otherhalogenated hydrocarbons, water, aliphatic hydrocarbons, gases, andsolid blowing agents, i.e., compounds that liberate gas as a result ofdesorption of gas. Typical chemical foaming/blowing agents includeinorganic agents, such as ammonium carbonate and carbonates of alkalimetals, and organic agents, such as azo and diazo compounds. Suitableazo compounds include, but are not limited to,2,2′-azobis(2-cyanobutane), 2,2′-azobis(methylbutyronitrile),azodicarbonamide, p,p′-oxybis(benzene sulfonyl hydrazide), p-toluenesulfonyl semicarbazide, and p-toluene sulfonyl hydrazide. Blowing agentsalso include CELOGEN foaming/blowing agents from Lion Copolymer; OPEXfoaming/blowing agents from Chemtura Corporation; nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, triazole and tetrazole derivatives, sulfonyl semicarbazides,urea derivatives, guanidine derivatives, and esters such asalkoxyboroxines. Blowing agents also include agents that liberate gassesas a result of chemical interaction between components, such as mixturesof acids and metals, mixtures of organic acids and inorganic carbonates,mixture of nitrites and ammonium salts, and the hydrolytic decompositionof urea. Suitable foaming/blowing agents also include expandablemicrospheres, such as EXPANCEL microspheres from Akzo Nobel.

The specific gravity of each of the cover layers is from 0.50 g/cm³ to5.00 g/cm³. Cover layers having an increased specific gravity preferablyhave a specific gravity of 0.95 g/cm³ or greater, or 1.00 g/cm³ orgreater, or 1.05 g/cm³ or greater, or 1.10 g/cm³ or greater, or 1.20g/cm³ or greater, or 1.30 g/cm³ or greater, or 1.40 g/cm³ or greater.Cover layers having a reduced specific gravity preferably have aspecific gravity of 1.05 g/cm³ or less, or 0.95 g/cm³ or less, or 0.90g/cm³ or less, or 0.85 g/cm³ or less. In a particular embodiment, thespecific gravity of inner cover is 0.95 g/cm³ or greater, or greaterthan 1.05 g/cm³, or 1.15 g/cm³ or greater; and the specific gravity ofthe outer cover layer is 1.30 g/cc or less, or 1.20 g/cm³ or less, orfrom 0.90 g/cm³ to 1.20 g/cm³. In a particular aspect of thisembodiment, the specific gravity of the outer cover layer is less thanthe specific gravity of the intermediate layer. In another particularaspect of this embodiment, the inner core is formed from a compositionwherein the specific gravity has been decreased; and the outer corelayer is formed from a composition wherein the specific gravity has beenincreased, preferably with tungsten filler. The weight distribution ofcore and cover layers disclosed herein can be varied to achieve certaindesired parameters, such as spin rate, compression, and initialvelocity.

The core preferably has an overall diameter of 1.25 inches or greater,or 1.35 inches or greater, or 1.390 inches or greater, or 1.45 inches orgreater, or an overall diameter within a range having a lower limit of0.25 or 0.50 or 0.75 or 1.00 or 1.25 or 1.35 or 1.39 or 1.40 or 1.44inches and an upper limit of 1.46 or 1.49 or 1.50 or 1.55 or 1.58 or1.60 inches.

The core has a center hardness within a range having a lower limit of 20or 25 or 30 or 35 or 40 or 45 or 50 or 55 Shore C and an upper limit of60 or 65 or 70 or 75 or 90 Shore C. The core has an outer surfacehardness within a range having a lower limit of 20 or 50 or 70 or 75Shore C and an upper limit of 75 or 80 or 85 or 90 or 95 Shore C.

The core has a negative hardness gradient, a zero hardness gradient, ora positive hardness gradient of up to 45 Shore C. Preferably, the centerhas a positive hardness gradient wherein the difference between thecenter hardness and the surface hardness of the center is from 10 to 45Shore C.

The core has an overall compression of 90 or less, or 80 or less, or 70or less, or 60 or less, or 50 or less, or 40 or less, or 20 or less, ora compression within a range having a lower limit of 10 or 20 or 30 or35 or 40 and an upper limit of 50 or 60 or 70 or 80 or 90.

One or more optional outer core layers are formed from thermoset orthermoplastic compositions and have a thickness within a range having alower limit of 0.005 or 0.01 or 0.02 or 0.04 inches and an upper limitof 0.05 or 0.10 or 0.20 or 0.30 or 0.40 inches In one embodiment, theouter core layer has a surface hardness of 45 Shore C or greater, or 70Shore C or greater, or 75 Shore C or greater, or 80 Shore C or greater,or a surface hardness within a range having a lower limit of 45 or 70 or80 Shore C and an upper limit of 90 or 95 Shore C. In a particularaspect of this embodiment, the surface hardness of the outer core layeris greater than the surface hardness of the center. In anotherparticular aspect of this embodiment, the surface hardness of the outercore layer is less than the surface hardness of the center. In anotherembodiment, the outer core layer has a surface hardness within a rangehaving a lower limit of 50 or 60 or 65 Shore C and an upper limit of 70or 75 or 80 Shore C. In a particular aspect of this embodiment, thesurface hardness of the outer core layer is less than the surfacehardness of the center.

In another embodiment, the outer core layer has a surface hardness of 20Shore C or greater, or 30 Shore C or greater, or 35 Shore C or greater,or 40 Shore C or greater, or a surface hardness within a range having alower limit of 20 or 30 or 35 or 40 or 50 Shore C and an upper limit of60 or 70 or 80 Shore C. In a particular aspect of this embodiment, theouter core layer is formed from a rubber composition selected from thosedisclosed in U.S. Patent Application Publication Nos. 2009/0011857 and2009/0011862, the entire disclosures of which are hereby incorporatedherein by reference.

Golf ball cores of the present invention typically have a coefficient ofrestitution (“COR”) at 125 ft/s of at least 0.750, or at least 0.775 orat least 0.780, or at least 0.782, or at least 0.785, or at least 0.787,or at least 0.790, or at least 0.795, or at least 0.798, or at least0.800.

Suitable outer cover materials include, but are not limited to, ionomerresins and blends thereof (e.g., SURLYN ionomer resins and DuPont HPF1000 and HPF 2000; IOTEK ionomers from ExxonMobil; AMPLIFY IO ionomersof ethylene acrylic acid copolymers from Dow; and CLARIX ionomer resinsfrom Schulman); polyurethanes; polyureas; copolymers and hybrids ofpolyurethane and polyurea; polyethylene, including, for example, lowdensity polyethylene, linear low density polyethylene, and high densitypolyethylene; polypropylene; rubber-toughened olefin polymers; acidcopolymers, e.g., (meth)acrylic acid, which do not become part of anionomeric copolymer; plastomers; flexomers; styrene/butadiene/styreneblock copolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; ethylene vinyl acetates; ethylenemethyl acrylates; polyvinyl chloride resins; polyamides, amide-esterelastomers, and graft copolymers of ionomer and polyamide, including,for example, PEBAX thermoplastic polyether block amides from Arkema,Inc.; crosslinked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as HYTREL from DuPont; polyurethane-basedthermoplastic elastomers, such as ELASTOLLAN from BASF; synthetic ornatural vulcanized rubber; and combinations thereof. In a particularembodiment, the cover is a single layer formed from a compositionselected from the group consisting of ionomers, polyester elastomers,polyamide elastomers, and combinations of two or more thereof.

Compositions comprising an ionomer or a blend of two or more ionomersare particularly suitable cover materials. Preferred ionomeric outercover compositions include: (a) a composition comprising a “high acidionomer” (i.e., having an acid content of greater than 16 wt %), such asSURLYN 8150; (b) a composition comprising a high acid ionomer and amaleic anhydride-grafted non-ionomeric polymer (e.g., FUSABONDfunctionalized polymers). A particularly preferred blend of high acidionomer and maleic anhydride-grafted polymer is a 84 wt %/16 wt % blendof SURLYN 8150 and FUSABOND; c) a composition comprising a 50/45/5 blendof SURLYN 8940/SURLYN 9650/NUCREL 960, preferably having a materialhardness of from 80 to 85 Shore C; (d) a composition comprising a50/25/25 blend of SURLYN® 8940/SURLYN 9650/SURLYN 9910, preferablyhaving a material hardness of about 90 Shore C; (e) a compositioncomprising a 50/50 blend of SURLYN 8940/SURLYN 9650, preferably having amaterial hardness of about 86 Shore C; (f) a composition comprising ablend of SURLYN 7940/SURLYN 8940, optionally including a melt flowmodifier; (g) a composition comprising a blend of a first high acidionomer and a second high acid ionomer, wherein the first high acidionomer is neutralized with a different cation than the second high acidionomer (e.g., 50/50 blend of SURLYN 8150 and SURLYN 9150), optionallyincluding one or more melt flow modifiers such as an ionomer,ethylene-acid copolymer or ester terpolymer; and (h) a compositioncomprising a blend of a first high acid ionomer and a second high acidionomer, wherein the first high acid ionomer is neutralized with adifferent cation than the second high acid ionomer, and from 0 to 10 wt% of an ethylene/acid/ester ionomer wherein the ethylene/acid/esterionomer is neutralized with the same cation as either the first highacid ionomer or the second high acid ionomer or a different cation thanthe first and second high acid ionomers (e.g., a blend of 40-50 wt %SURLYN 8140, 40-50 wt % SURLYN 9120, and 0-10 wt % SURLYN 6320).

Ionomeric outer cover compositions can be blended with non-ionicthermoplastic resins, particularly to manipulate product properties.Examples of suitable non-ionic thermoplastic resins include, but are notlimited to, polyurethane, poly-ether-ester, poly-amide-ether,polyether-urea, thermoplastic polyether block amides (e.g., PEBAX blockcopolymers from Arkema, Inc.), styrene-butadiene-styrene blockcopolymers, styrene(ethylene-butylene)-styrene block copolymers,polyamides, polyesters, polyolefins (e.g., polyethylene, polypropylene,ethylene-propylene copolymers, polyethylene-(meth)acrylate,plyethylene-(meth)acrylic acid, functionalized polymers with maleicanhydride grafting, FUSABOND functionalized polymers from DuPont,functionalized polymers with epoxidation, elastomers (e.g., ethylenepropylene diene monomer rubber, metallocene-catalyzed polyolefin) andground powders of thermoset elastomers.

Ionomer golf ball outer cover compositions may include a flow modifier,such as, but not limited to, NUCREL acid copolymer resins, andparticularly NUCREL 960, from DuPont.

Polyurethanes, polyureas, and blends and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

While the inventive golf ball may be formed from a variety of differingcover materials, preferred outer cover layer materials include, but arenot limited to, (1) polyurethanes, such as those prepared from polyolsor polyamines and diisocyanates or polyisocyanates and/or theirprepolymers, and those disclosed in U.S. Pat. Nos. 5,334,673 and6,506,851; (2) polyureas, such as those disclosed in U.S. Pat. Nos.5,484,870 and 6,835,794; (3) polyurethane-urea hybrids, blends orcopolymers comprising urethane or urea segments; and (4) other suitablepolyurethane compositions comprising a reaction product of at least onepolyisocyanate and at least one curing agent are disclosed in U.S. Pat.Nos. 7,105,610 and 7,491,787, all of which are incorporated herein byreference.

Suitable polyurethane compositions comprise a reaction product of atleast one polyisocyanate and at least one curing agent. The curing agentcan include, for example, one or more polyamines, one or more polyols,or a combination thereof. The polyisocyanate can be combined with one ormore polyols to form a prepolymer, which is then combined with the atleast one curing agent. Thus, the polyols described herein are suitablefor use in one or both components of the polyurethane material, i.e., aspart of a prepolymer and in the curing agent. Suitable polyurethanes aredescribed in U.S. Pat. No. 7,331,878, which is incorporated by referencein its entirety.

Exemplary polyisocyanates suitable for use in the outer cover layers ofthe invention include, but are not limited to, 4,4′-diphenylmethanediisocyanate (“MDI”); polymeric MDI; carbodiimide-modified liquid MDI;4,4′-dicyclohexylmethane diisocyanate; p-phenylene diisocyanate(“PPDI”); m-phenylene diisocyanate; toluene diisocyanate (“TDI”);3,3′-dimethyl-4,4′-biphenylene diisocyanate; isophoronediisocyanate;1,6-hexamethylene diisocyanate (“HDI”); naphthalene diisocyanate; xylenediisocyanate; p-tetramethylxylene diisocyanate; m-tetramethylxylenediisocyanate; ethylene diisocyanate; propylene-1,2-diisocyanate;tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate;dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate; tetracene diisocyanate;napthalene diisocyanate; anthracene diisocyanate; isocyanurate oftoluene diisocyanate; uretdione of hexamethylene diisocyanate; andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g.,di-isocyanate, tri-isocyanate, and tetra-isocyanate. Preferably, thepolyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and morepreferably, the polyisocyanate includes MDI. It should be understoodthat, as used herein, the term MDI includes 4,4′-diphenylmethanediisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, andmixtures thereof and, additionally, that the diisocyanate employed maybe “low free monomer,” understood by one of ordinary skill in the art tohave lower levels of “free” monomer isocyanate groups, typically lessthan about 0.1% free monomer isocyanate groups. Examples of “low freemonomer” diisocyanates include, but are not limited to Low Free MonomerMDI, Low Free Monomer TDI, and Low Free Monomer PPDI.

The at least one polyisocyanate should have less than about 14%unreacted NCO groups. Preferably, the at least one polyisocyanate has nogreater than about 8.0% NCO, more preferably no greater than about 7.8%,and most preferably no greater than about 7.5% NCO with a level of NCOof about 7.2 or 7.0, or 6.5% NCO commonly used.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in thepolyurethane material. Suitable polyester polyols include, but are notlimited to, polyethylene adipate glycol; polybutylene adipate glycol;polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol;poly(hexamethylene adipate) glycol; and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polycaprolactone polyols include,but are not limited to, 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, polycarbonate polyols are included in thepolyurethane material of the invention. Suitable polycarbonates include,but are not limited to, polyphthalate carbonate and poly(hexamethylenecarbonate) glycol. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups. In one embodiment, the molecular weight of the polyol is fromabout 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethanecomposition of the invention and have been found to improve cut, shear,and impact resistance of the resultant balls. Preferred polyaminecuratives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyl diaminodiphenyl methane; p,p′-methylene dianiline; m-phenylenediamine;4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-methylene-bis-(2,3-dichloroaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE 300, from Albermarle Corporationof Baton Rouge, La. Suitable polyamine curatives, which include bothprimary and secondary amines, preferably have molecular weights rangingfrom about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curativesmay be added to the aforementioned polyurethane composition. Suitablediol, triol, and tetraol groups include ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; polypropylene glycol;lower molecular weight PTMEG; 1,3-bis(2-hydroxyethoxy) benzene;1,3-bis-[2-(2-hydroxyethoxy) ethoxy] benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy} benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol;resorcinol-di-(.beta.-hydroxyethyl)ether;hydroquinone-di-(.beta.-hydroxyethyl)ether; and mixtures thereof.Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy} benzene; 1,4-butanediol,and mixtures thereof. Preferably, the hydroxy-terminated curatives havemolecular weights ranging from about 48 to 2000. It should be understoodthat molecular weight, as used herein, is the absolute weight averagemolecular weight.

Both the hydroxy-terminated and amine curatives can include one or moresaturated, unsaturated, aromatic, and cyclic groups. Additionally, thehydroxy-terminated and amine curatives can include one or more halogengroups. The polyurethane composition can be formed with a blend ormixture of curing agents. If desired, however, the polyurethanecomposition may be formed with a single curing agent.

In a preferred embodiment of the present invention, saturatedpolyurethanes are used to form one or more of the cover layers,preferably the outer cover layer, and may be selected from among bothcastable thermoset and thermoplastic polyurethanes.

In this embodiment, the saturated polyurethanes of the present inventionare substantially free of aromatic groups or moieties. Saturatedpolyurethanes suitable for use in the invention are a product of areaction between at least one polyurethane prepolymer and at least onesaturated curing agent. The polyurethane prepolymer is a product formedby a reaction between at least one saturated polyol and at least onesaturated diisocyanate. A catalyst may be employed to promote thereaction between the curing agent and the isocyanate and polyol, or thecuring agent and the prepolymer.

Saturated diisocyanates which can be used include, without limitation,ethylene diisocyanate; propylene-1,2-diisocyanate;tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate;2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylenediisocyanate; dodecane-1,12-diisocyanate; dicyclohexylmethanediisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; isophoronediisocyanate; methyl cyclohexylene diisocyanate; triisocyanate of HDI;triisocyanate of 2,2,4-trimethyl-1,6-hexane diisocyanate. The mostpreferred saturated diisocyanates are 4,4′-dicyclohexylmethanediisocyanate and isophorone diisocyanate.

Saturated polyols are appropriate for use in this invention and include,without limitation, polyether polyols such as PTMEG andpoly(oxypropylene) glycol. Suitable saturated polyester polyols includepolyethylene adipate glycol, polyethylene propylene adipate glycol,polybutylene adipate glycol, polycarbonate polyol and ethyleneoxide-capped polyoxypropylene diols. Saturated polycaprolactone polyolswhich are useful in the invention include diethylene glycol-initiatedpolycaprolactone, 1,4-butanediol-initiated polycaprolactone,1,6-hexanediol-initiated polycaprolactone; trimethylol propane-initiatedpolycaprolactone, neopentyl glycol initiated polycaprolactone, andPTMEG-initiated polycaprolactone. The most preferred saturated polyolsare PTMEG and PTMEG-initiated polycaprolactone.

Suitable saturated curatives include 1,4-butanediol, ethylene glycol,diethylene glycol, PTMEG, propylene glycol; trimethanolpropane;tetra-(2-hydroxypropyl)-ethylenediamine; isomers and mixtures of isomersof cyclohexyldimethylol, isomers and mixtures of isomers of cyclohexanebis(methylamine); triisopropanolamine; ethylene diamine; diethylenetriamine; triethylene tetramine; tetraethylene pentamine;4,4′-dicyclohexylmethane diamine; 2,2,4-trimethyl-1,6-hexanediamine;2,4,4-trimethyl-1,6-hexanediamine; diethyleneglycoldi-(aminopropyl)ether; 4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,2-bis-(sec-butylamino)cyclohexane; 1,4-bis-(sec-butyl amino)cyclohexane; isophorone diamine; hexamethylene diamine; propylenediamine; 1-methyl-2,4-cyclohexyl diamine; 1-methyl-2,6-cyclohexyldiamine; 1,3-diaminopropane; dimethylamino propylamine; diethylaminopropylamine; imido-bis-propylamine; isomers and mixtures of isomers ofdiaminocyclohexane; monoethanolamine; diethanolamine; triethanolamine;monoisopropanolamine; and diisopropanolamine. The most preferredsaturated curatives are 1,4-butanediol, 1,4-cyclohexyldimethylol and4,4′-bis-(sec-butylamino)-dicyclohexylmethane.

Alternatively, other suitable polymers include partially- orfully-neutralized ionomer, metallocene, or other single-site catalyzedpolymer, polyester, polyamide, non-ionomeric thermoplastic elastomer,copolyether-esters, copolyether-amides, polycarbonate, polybutadiene,polyisoprene, polystryrene block copolymers (such asstyrene-butadiene-styrene), styrene-ethylene-propylene-styrene,styrene-ethylene-butylene-styrene, and the like, and blends thereof.Thermosetting polyurethanes or polyureas are suitable for outer coverlayers.

Additionally, polyurethane can be replaced with or blended with apolyurea material. Polyureas are distinctly different from polyurethanecompositions, but also result in desirable aerodynamic and aestheticcharacteristics when used in golf ball components. The polyurea-basedcompositions are preferably saturated in nature.

Without being bound to any particular theory, it is now believed thatsubstitution of the long chain polyol segment in the polyurethaneprepolymer with a long chain polyamine oligomer soft segment to form apolyurea prepolymer, improves shear, cut, and resiliency, as well asadhesion to other components. Thus, the polyurea compositions of thisinvention may be formed from the reaction product of an isocyanate andpolyamine prepolymer crosslinked with a curing agent. For example,polyurea-based compositions of the invention may be prepared from atleast one isocyanate, at least one polyether amine, and at least onediol curing agent or at least one diamine curing agent.

Any polyamine available to one of ordinary skill in the art is suitablefor use in the polyurea prepolymer. Polyether amines are particularlysuitable for use in the prepolymer. As used herein, “polyether amines”refer to at least polyoxyalkyleneamines containing primary amino groupsattached to the terminus of a polyether backbone. Due to the rapidreaction of isocyanate and amine, and the insolubility of many ureaproducts, however, the selection of diamines and polyether amines islimited to those allowing the successful formation of the polyureaprepolymers. In one embodiment, the polyether backbone is based ontetramethylene, propylene, ethylene, trimethylolpropane, glycerin, andmixtures thereof.

Suitable polyether amines include, but are not limited to,methyldiethanolamine; polyoxyalkylenediamines such as,polytetramethylene ether diamines, polyoxypropylenetriamine, andpolyoxypropylene diamines; poly(ethylene oxide capped oxypropylene)ether diamines; propylene oxide-based triamines;triethyleneglycoldiamines; trimethylolpropane-based triamines;glycerin-based triamines; and mixtures thereof. In one embodiment, thepolyether amine used to form the prepolymer is JEFFAMINE D2000 fromHuntsman Chemical Co. of Austin, Tex.

The molecular weight of the polyether amine for use in the polyureaprepolymer may range from about 100 to about 5000. In one embodiment,the polyether amine molecular weight is about 200 or greater, preferablyabout 230 or greater. In another embodiment, the molecular weight of thepolyether amine is about 4000 or less. In yet another embodiment, themolecular weight of the polyether amine is about 600 or greater. Instill another embodiment, the molecular weight of the polyether amine isabout 3000 or less. In yet another embodiment, the molecular weight ofthe polyether amine is between about 1000 and about 3000, morepreferably is between about 1500 to about 2500, and most preferably from2000 to 2500. Because lower molecular weight polyether amines may beprone to forming solid polyureas, a higher molecular weight oligomer,such as JEFFAMINE D2000, is preferred.

Other suitable castable polyurea compositions for use in the golf ballsof the present invention include those formed from the reaction productof a prepolymer formed from an isocyanate and an amine-terminated PTMEGand an amine-terminated curing agent, and those formed from the reactionproduct of a polyurea prepolymer cured with an amine-terminated PTMEG.In either scenario, the amine-terminated PTMEG is terminated withsecondary amines. In addition, the amine-terminated PTMEG may be acopolymer with polypropylene glycol, wherein the PTMEG is end-cappedwith one or more propylene glycol units to form the copolymer.

Another suitable composition includes a prepolymer including thereaction product of an isocyanate-containing component and anamine-terminated component, wherein the amine-terminated componentincludes a copolymer of PTMEG and polypropylene glycol including atleast one terminal amino group; and an amine-terminated curing agent. Inthis aspect of the invention the prepolymer may include about 4% toabout 9% NCO groups by weight of the prepolymer.

In one embodiment, the at least one terminal amino group includessecondary amines. In another embodiment, the at least one terminal aminogroup includes a terminal secondary amino group at both ends of thecopolymer. In yet another embodiment, the amine-terminated curing agentincludes a secondary diamine.

The polyureas of the present invention also include a polyureacomposition formed from a prepolymer formed from the reaction product ofan isocyanate-containing compound and an isocyanate-reactive compound,wherein the isocyanate-reactive compound includes PTMEG homopolymerhaving a molecular weight of about 1800 to 2200 and terminal secondaryamino groups; and an amine-terminated curing agent. In this aspect ofthe invention, the prepolymer may include about 6% to about 8% NCOgroups by weight of the prepolymer. In addition, the PTMEG homopolymermay have a molecular weight of about 1900 to about 2100. In oneembodiment, the amine-terminated curing agent includes a secondarydiamine.

In one embodiment, the polyalkylene glycol includes polypropyleneglycol, polyethylene glycol, and copolymers or mixtures thereof. Inanother embodiment, the amino groups include secondary amino groups. Theamine-terminated curing agent may include an amine-terminated PTMEG. Inone embodiment, the amine-terminated PTMEG includes at least oneterminal secondary amino group.

Conventional aromatic polyurethane/urethane elastomers andpolyurethane/urea elastomers are generally prepared by curing aprepolymer of diisocyanate and long chain polyol with at least one diolcuring agent or at least one diamine curing agent, respectively. Incontrast, the use of a long chain amine-terminated compound to form apolyurea prepolymer has been shown to improve shear, cut, andresiliency, as well as adhesion to other components.

The use of an amine-terminated PTMEG and/or an amine-terminatedcopolymer of PTMEG and polypropylene glycol (“PPG”) in the prepolymer oras a curing agent provide enhanced shear, cut, and resiliency ascompared to conventional polyurea elastomers. For example, thecompositions of the invention have improved durability and performancecharacteristics over that of a polyurea composition formed withamine-terminated PPG.

The polyurea-based compositions of this invention may be formed inseveral ways: a) from a prepolymer that is the reaction product of anisocyanate-containing component and amine-terminated PTMEG chainextended with a curing agent; b) from a prepolymer that is the reactionproduct of an isocyanate-containing component and an amine-terminatedcopolymer of PTMEG and PPG chain extended with a curing agent; c) from aprepolymer that is the reaction product of a polyurea-based prepolymerchain extended with an amine-terminated PTMEG; and d) from a prepolymerthat is the reaction product of a polyurea-based prepolymer chainextended with an amine-terminated copolymer of PTMEG and PPG.

For example, the compositions of the invention may be prepared from atleast one isocyanate-containing component, at least one amine-terminatedcopolymer of PTMEG and PPG, preferably a secondary diamine, and at leastone amine-terminated curing agent, preferably a secondary aliphaticdiamine or primary aromatic diamine curing agent. The presence of PTMEGin the backbone provides better shear resistance as compared to abackbone including only PPG. Commercially-available amine-terminatedPTMEG and/or copolymer of PTMEG and PPG include those sold by HuntsmanChemical under the tradenames XTJ-559, XTG-604, XTG-605, and XTG-653.

As briefly discussed above, some amines may be unsuitable for reactionwith the isocyanate because of the rapid reaction between the twocomponents. In particular, shorter chain amines are fast reacting. Inone embodiment, however, a hindered secondary diamine may be suitablefor use in the prepolymer. It is believed that an amine with a highlevel of stearic hindrance, e.g., a tertiary butyl group on the nitrogenatom, has a slower reaction rate than an amine with no hindrance or alow level of hindrance. For example,4,4′-bis-(sec-butylamino)-dicyclohexylmethane (CLEARLINK 1000) may besuitable for use in combination with an isocyanate to form the polyureaprepolymer.

Any isocyanate available to one of ordinary skill in the art is suitablefor use in the polyurea prepolymer. Isocyanates for use with the presentinvention include aliphatic, cycloaliphatic, araliphatic, aromatic, anyderivatives thereof, and combinations of these compounds having two ormore isocyanate groups per molecule. The isocyanates may be organicpolyisocyanate-terminated prepolymers. The isocyanate-containingreactable component may also include any isocyanate-functional monomer,dimer, trimer, or multimeric adduct thereof, prepolymer,quasi-prepolymer, or mixtures thereof. Isocyanate-functional compoundsmay include monoisocyanates or polyisocyanates that include anyisocyanate functionality of two or more.

Suitable isocyanate-containing components include diisocyanates havingthe generic structure: O═C═N—R—N═C═O, where R is preferably a cyclic,aromatic, or linear or branched hydrocarbon moiety containing from about1 to about 20 carbon atoms. The diisocyanate may also contain one ormore cyclic groups or one or more phenyl groups. When multiple cyclic oraromatic groups are present, linear and/or branched hydrocarbonscontaining from about 1 to about 10 carbon atoms can be present asspacers between the cyclic or aromatic groups. In some cases, the cyclicor aromatic group(s) may be substituted at the 2-, 3-, and/or4-positions, or at the ortho-, meta-, and/or para-positions,respectively. Substituted groups may include, but are not limited to,halogens, primary, secondary, or tertiary hydrocarbon groups, or amixture thereof. Copolymeric isocyanates, such as Bayer DESMODUR HL,which is a copolymer of TDI and HDI, are preferred.

Examples of diisocyanates that can be used with the present inventioninclude, but are not limited to, substituted and isomeric mixturesincluding 2,2′-, 2,4′-, and 4,4′-diphenylmethane diisocyanate;3,3′-dimethyl-4,4′-biphenylene diisocyanate; toluene diisocyanate;polymeric MDI; carbodiimide-modified liquid 4,4′-diphenylmethanediisocyanate; p-phenylene diisocyanate; m-phenylene diisocyanate;triphenyl methane-4,4′- and triphenyl methane-4,4′-triisocyanate;naphthylene-1,5-diisocyanate; 2,4′-, 4,4′-, and 2,2-biphenyldiisocyanate; polyphenyl polymethylene polyisocyanate; mixtures of MDIand PMDI; mixtures of PMDI and TDI; ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene-1,2-diisocyanate;tetramethylene-1,3-diisocyanate; tetramethylene-1,4-diisocyanate;1,6-hexamethylene-diisocyanate; octamethylene diisocyanate;decamethylene diisocyanate; 2,2,4-trimethylhexamethylene diisocyanate;2,4,4-trimethylhexamethylene diisocyanate; dodecane-1,12-diisocyanate;cyclobutane-1,3-diisocyanate; cyclohexane-1,2-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;methyl-cyclohexylene diisocyanate; 2,4-methylcyclohexane diisocyanate;2,6-methyl cyclohexane diisocyanate; 4,4′-dicyclohexyl diisocyanate;2,4′-dicyclohexyl diisocyanate; 1,3,5-cyclohexane triisocyanate;isocyanatomethylcyclohexane isocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane;isocyanatoethylcyclohexane isocyanate; bis(isocyanatomethyl)-cyclohexanediisocyanate; 4,4′-bis(isocyanatomethyl) dicyclohexane;2,4′-bis(isocyanatomethyl) dicyclohexane; isophorone diisocyanate;triisocyanate of HDI; triisocyanate of 2,2,4-trimethyl-1,6-hexanediisocyanate; 4,4′ dicyclohexylmethane diisocyanate;2,4-hexahydrotoluene diisocyanate; 2,6-hexahydrotoluene diisocyanate;1,2-, 1,3-, and 1,4-phenylene diisocyanate; aromatic aliphaticisocyanate, such as 1,2-, 1,3-, and 1,4-xylene diisocyanate;m-tetramethylxylene diisocyanate; p-tetramethylxylene diisocyanate;trimerized isocyanurate of any polyisocyanate, such as isocyanurate oftoluene diisocyanate; trimer of diphenylmethane diisocyanate; trimer oftetramethylxylene diisocyanate; isocyanurate of hexamethylenediisocyanate; isocyanurate of isophorone diisocyanate; and mixturesthereof; dimerized uredione of any polyisocyanate, such as uretdione oftoluene diisocyanate; uretdione of hexamethylene diisocyanate; andmixtures thereof; modified polyisocyanate derived from the aboveisocyanates and polyisocyanates; and mixtures thereof.

Examples of saturated diisocyanates that can be used with the presentinvention include, but are not limited to, ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene diisocyanate;tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate;octamethylene diisocyanate; decamethylene diisocyanate;2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylenediisocyanate; dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,2-diisocyanate; cyclohexane-1,3-diisocyanate;cyclohexane-1,4-diisocyanate; methyl-cyclohexylene diisocyanate;2,4-methylcyclohexane diisocyanate; 2,6-methylcyclohexane diisocyanate;4,4′-dicyclohexyl diisocyanate; 2,4′-dicyclohexyl diisocyanate;1,3,5-cyclohexane triisocyanate; isocyanatomethylcyclohexane isocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane;isocyanatoethylcyclohexane isocyanate; bis(isocyanatomethyl)-cyclohexanediisocyanate; 4,4′-bis(isocyanatomethyl) dicyclohexane;2,4′-bis(isocyanatomethyl) dicyclohexane; isophorone diisocyanate;triisocyanate of HDI; triisocyanate of 2,2,4-trimethyl-1,6-hexanediisocyanate; 4,4′ dicyclohexylmethane diisocyanate;2,4-hexahydrotoluene diisocyanate; 2,6-hexahydrotoluene diisocyanate;and mixtures thereof. Aromatic aliphatic isocyanates may also be used toform light stable materials. Examples of such isocyanates include 1,2-,1,3-, and 1,4-xylene diisocyanate; meta-tetramethylxylene diisocyanate;p-tetramethylxylene diisocyanate; trimerized isocyanurate of anypolyisocyanate, such as isocyanurate of toluene diisocyanate, trimer ofdiphenylmethane diisocyanate, trimer of tetramethylxylene diisocyanate,isocyanurate of hexamethylene diisocyanate, isocyanurate of isophoronediisocyanate, and mixtures thereof; dimerized uredione of anypolyisocyanate, such as uretdione of toluene diisocyanate, uretdione ofhexamethylene diisocyanate, and mixtures thereof; modifiedpolyisocyanate derived from the above isocyanates and polyisocyanates;and mixtures thereof. In addition, the aromatic aliphatic isocyanatesmay be mixed with any of the saturated isocyanates listed above for thepurposes of this invention.

The number of unreacted NCO groups in the polyurea prepolymer ofisocyanate and polyether amine may be varied to control such factors asthe speed of the reaction, the resultant hardness of the composition,and the like. For example, the number of unreacted NCO groups in thepolyurea prepolymer of isocyanate and polyether amine may be less thanabout 14%. In one embodiment, the polyurea prepolymer has from about 5%to 11% unreacted NCO groups, preferably from about 6% to 9.5% unreactedNCO groups. In one embodiment, the percentage of unreacted NCO groups isabout 3% to 9%. Alternatively, the percentage of unreacted NCO groups inthe polyurea prepolymer may be about 7.5% or less, more preferably,about 7% or less. In another embodiment, the unreacted NCO content isfrom about 2.5% to 7.5%, more preferably from about 4% to 6.5%.

When formed, polyurea prepolymers may contain about 10% to 20% by weightof the prepolymer of free isocyanate monomer. Thus, in one embodiment,the polyurea prepolymer may be stripped of the free isocyanate monomer.For example, after stripping, the prepolymer may contain about 1% orless free isocyanate monomer. In another embodiment, the prepolymercontains about 0.5% by weight or less of free isocyanate monomer.

The polyether amine may be blended with additional polyols to formulatecopolymers that are reacted with excess isocyanate to form the polyureaprepolymer. In one embodiment, less than about 30% polyol by weight ofthe copolymer is blended with the saturated polyether amine. In anotherembodiment, less than about 20% polyol by weight of the copolymer,preferably less than about 15% by weight of the copolymer, is blendedwith the polyether amine. The polyols listed above with respect to thepolyurethane prepolymer, e.g., polyether polyols, polycaprolactonepolyols, polyester polyols, polycarbonate polyols, hydrocarbon polyols,other polyols, and mixtures thereof, are also suitable for blending withthe polyether amine. The molecular weight of these polymers may be fromabout 200 to about 4000, but also may be from about 1000 to about 3000,and more preferably are from about 1500 to about 2500.

The polyurea composition can be formed by crosslinking the polyureaprepolymer with a single curing agent or a blend of curing agents. Thecuring agent of the invention is preferably an amine-terminated curingagent, more preferably a secondary diamine curing agent so that thecomposition contains only urea linkages. In one embodiment, theamine-terminated curing agent may have a molecular weight of about 64 orgreater. In another embodiment, the molecular weight of the amine-curingagent is about 2000 or less. As discussed above, certainamine-terminated curing agents may be modified with a compatibleamine-terminated freezing point depressing agent or mixture ofcompatible freezing point depressing agents.

Suitable amine-terminated curing agents include, but are not limited to,ethylene diamine; hexamethylene diamine; 1-methyl-2,6-cyclohexyldiamine; tetrahydroxypropylene ethylene diamine; 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,4-bis-(sec-butylamino)-cyclohexane;1,2-bis-(sec-butylamino)-cyclohexane; derivatives of4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 4,4′-dicyclohexylmethanediamine; 1,4-cyclohexane-bis-(methylamine);1,3-cyclohexane-bis-(methylamine); diethylene glycoldi-(aminopropyl)ether; 2-methylpentamethylene-diamine;diaminocyclohexane; diethylene triamine; triethylene tetramine;tetraethylene pentamine; propylene diamine; 1,3-diaminopropane;dimethylamino propylamine; diethylamino propylamine; dipropylenetriamine; imido-bis-propylamine; monoethanolamine, diethanolamine;triethanolamine; monoisopropanolamine, diisopropanolamine;isophoronediamine; 4,4′-methylenebis-(2-chloroaniline);3,5;dimethylthio-2,4-toluenediamine;3,5-dimethylthio-2,6-toluenediamine; 3,5-diethylthio-2,4-toluenediamine;3,5-diethylthio-2,6-toluenediamine;4,4′-bis-(sec-butylamino)-diphenylmethane and derivatives thereof;1,4-bis-(sec-butylamino)-benzene; 1,2-bis-(sec-butylamino)-benzene;N,N′-dialkylamino-diphenylmethane; N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylene diamine;trimethyleneglycol-di-p-aminobenzoate;polytetramethyleneoxide-di-p-aminobenzoate;4,4′-methylenebis-(3-chloro-2,6-diethyleneaniline);4,4′-methylenebis-(2,6-diethylaniline); m-phenylenediamine;paraphenylenediamine; and mixtures thereof. In one embodiment, theamine-terminated curing agent is4,4′-bis-(sec-butylamino)-dicyclohexylmethane.

Suitable saturated amine-terminated curing agents include, but are notlimited to, ethylene diamine; hexamethylene diamine;1-methyl-2,6-cyclohexyl diamine; tetrahydroxypropylene ethylene diamine;2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,4-bis-(sec-butylamino)-cyclohexane;1,2-bis-(sec-butylamino)-cyclohexane; derivatives of4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 4,4′-dicyclohexylmethanediamine; 4,4′-methylenebis-(2,6-diethylaminocyclohexane;1,4-cyclohexane-bis-(methylamine); 1,3-cyclohexane-bis-(methylamine);diethylene glycol di-(aminopropyl)ether; 2-methylpentamethylene-diamine;diaminocyclohexane; diethylene triamine; triethylene tetramine;tetraethylene pentamine; propylene diamine; 1,3-diaminopropane;dimethylamino propylamine; diethylamino propylamine;imido-bis-propylamine; monoethanolamine, diethanolamine;triethanolamine; monoisopropanolamine, diisopropanolamine;isophoronediamine; triisopropanolamine; and mixtures thereof. Inaddition, any of the polyether amines listed above may be used as curingagents to react with the polyurea prepolymers.

Any method known to one of ordinary skill in the art may be used tocombine the polyisocyanate, polyol, and curing agent of the presentinvention. One commonly employed method, known in the art as a one-shotmethod, involves concurrent mixing of the polyisocyanate, polyol, andcuring agent. This method results in a mixture that is inhomogenous(more random) and affords the manufacturer less control over themolecular structure of the resultant composition. A preferred method ofmixing is known as a prepolymer method. In this method, thepolyisocyanate and the polyol are mixed separately prior to addition ofthe curing agent. This method affords a more homogeneous mixtureresulting in a more consistent polymer composition.

Due to the very thin nature, it has been found by the present inventionthat the use of a castable, reactive material, which is applied in afluid form, makes it possible to obtain very thin outer cover layers ongolf balls. Specifically, it has been found that castable, reactiveliquids, which react to form a urethane elastomer material, providedesirable very thin outer cover layers.

Cover compositions may include one or more filler(s), such as thefillers given above for rubber compositions of the present invention(e.g., titanium dioxide, barium sulfate, etc.), and/or additive(s), suchas coloring agents, fluorescent agents, whitening agents, antioxidants,dispersants, UV absorbers, light stabilizers, plasticizers, surfactants,compatibility agents, foaming agents, reinforcing agents, releaseagents, and the like.

The cover preferably has a surface hardness of 70 Shore D or less, or 65Shore D or less, or 60 Shore D or less, or 55 Shore D or less. The coverpreferably has a material hardness of 70 Shore D or less, or 65 Shore Dor less, or 60 Shore D or less, or 55 Shore D or less. Alternatively,the cover preferably has a surface hardness of 60 Shore D or greater, or65 Shore D or greater. The cover preferably has a material hardness of60 Shore D or greater, or 65 Shore D or greater.

In a particular embodiment, the cover is a dual- or multi-layer coverincluding an inner or intermediate cover layer formed from a compositionof the present invention and an outer cover layer formed from apolyurethane- or polyurea-based composition. The inner cover layerpreferably has a surface hardness of 70 Shore D or less, or 65 Shore Dor less, or less than 65 Shore D, or a Shore D hardness of from 50 to65, or a Shore D hardness of from 57 to 60, or a Shore D hardness of 58,and a thickness within a range having a lower limit of 0.010 or 0.020 or0.030 inches and an upper limit of 0.045 or 0.080 or 0.120 inches. Theouter cover layer is preferably formed from a castable or reactioninjection moldable polyurethane, polyurea, or copolymer or hybrid ofpolyurethane/polyurea. Such cover material is preferably thermosetting,but may be thermoplastic. The outer cover layer composition preferablyhas a material hardness of 85 Shore C or less, or 45 Shore D or less, or40 Shore D or less, or from 25 Shore D to 40 Shore D, or from 30 Shore Dto 40 Shore D. The outer cover layer preferably has a surface hardnesswithin a range having a lower limit of 20 or 30 or 35 or 40 Shore D andan upper limit of 52 or 58 or 60 or 65 or 70 or 72 or 75 Shore D. Theouter cover layer preferably has a thickness within a range having alower limit of 0.01 or 0.015 or 0.025 inches and an upper limit of 0.035or 0.04 or 0.045 or 0.05 or 0.055 or 0.075 or 0.08 or 0.115 inches.

A moisture vapor barrier layer is optionally employed between the coreand the cover. Moisture vapor barrier layers are further disclosed, forexample, in U.S. Pat. Nos. 6,632,147; and 7,182,702, the entiredisclosures of which are hereby incorporated herein by reference.

In addition to the materials disclosed above, any of the core or coverlayers may comprise one or more of the following materials as long asthey are not used at such a level as to negatively affect thermalstability of the blend, increase melt flow beyond a critical level, orotherwise work against the inventive objective disclosed herein:thermoplastic elastomer, thermoset elastomer, synthetic rubber,thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer,polycarbonate, polyolefin, polyamide, copolymeric polyamide, polyesters,polyester-amides, polyether-amides, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, metallocene-catalyzed polymers,styrene-acrylonitrile (“SAN”), olefin-modified SAN,acrylonitrile-styrene-acrylonitrile, styrene-maleic anhydride (“S/MA”)polymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer (“LCP”), ethylene-propylene-diene rubber(“EPDM”), ethylene-vinyl acetate copolymer (“EVA”), ethylene propylenerubber (“EPR”), ethylene vinyl acetate, polyurea, and polysiloxane.Suitable polyamides for use as an additional material in compositionsdisclosed herein also include resins obtained by: (1) polycondensationof (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacicacid, terephthalic acid, isophthalic acid or 1,4-cyclohexanedicarboxylicacid, with (b) a diamine, such as ethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, ordecamethylenediamine, 1,4-cyclohexyldiamine or m-xylylenediamine; (2) aring-opening polymerization of cyclic lactam, such as.epsilon.-caprolactam or co-laurolactam; (3) polycondensation of anaminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid,11-aminoundecanoic acid or 12-aminododecanoic acid; or (4)copolymerzation of a cyclic lactam with a dicarboxylic acid and adiamine. Specific examples of suitable polyamides include NYLON 6, NYLON66, NYLON 610, NYLON 11, NYLON 12, copolymerized NYLON, NYLON MXD6, andNYLON 46.

Other preferred materials suitable for use as an additional material ingolf ball compositions disclosed herein include SKYPEL polyesterelastomers from SK Chemicals of South Korea; SEPTON diblock and triblockcopolymers from Kuraray Corporation of Kurashiki, Japan; and KRATONdiblock and triblock copolymers from Kraton Polymers of Houston, Tex.

Ionomers are also well suited for blending with compositions disclosedherein. Suitable ionomeric polymers include .alpha.-olefin/unsaturatedcarboxylic acid copolymer- or terpolymer-type ionomeric resins.Copolymeric ionomers are obtained by neutralizing at least a portion ofthe carboxylic groups in a copolymer of an .alpha.-olefin and an.alpha.,.beta.-unsaturated carboxylic acid having from 3 to 8 carbonatoms, with a metal ion. Terpolymeric ionomers are obtained byneutralizing at least a portion of the carboxylic groups in a terpolymerof an .alpha.-olefin, an .alpha.,.beta.-unsaturated carboxylic acidhaving from 3 to 8 carbon atoms, and an .alpha.,.beta.-unsaturatedcarboxylate having from 2 to 22 carbon atoms, with a metal ion. Examplesof suitable .alpha.-olefins for copolymeric and terpolymeric ionomersinclude ethylene, propylene, 1-butene, and 1-hexene. Examples ofsuitable unsaturated carboxylic acids for copolymeric and terpolymericionomers include acrylic, methacrylic, ethacrylic,.alpha.-chloroacrylic, crotonic, maleic, fumaric, and itaconic acid.Copolymeric and terpolymeric ionomers include ionomers having variedacid contents and degrees of acid neutralization, neutralized bymonovalent or bivalent cations as disclosed herein.

Silicone materials are also well suited for blending with compositionsdisclosed herein. Suitable silicone materials include monomers,oligomers, prepolymers, and polymers, with or without adding reinforcingfiller. One type of silicone material that is suitable can incorporateat least one alkenyl group having at least 2 carbon atoms in theirmolecules. Examples of these alkenyl groups include, but are not limitedto, vinyl, allyl, butenyl, pentenyl, hexenyl, and decenyl. The alkenylfunctionality can be located at any location of the silicone structure,including one or both terminals of the structure. The remaining (i.e.,non-alkenyl) silicon-bonded organic groups in this component areindependently selected from hydrocarbon or halogenated hydrocarbongroups that contain no aliphatic unsaturation. Non-limiting examples ofthese include: alkyl groups, such as methyl, ethyl, propyl, butyl,pentyl, and hexyl; cycloalkyl groups, such as cyclohexyl andcycloheptyl; aryl groups, such as phenyl, tolyl, and xylyl; aralkylgroups, such as benzyl and phenethyl; and halogenated alkyl groups, suchas 3,3,3-trifluoropropyl and chloromethyl. Another type of suitablesilicone material is one having hydrocarbon groups that lack aliphaticunsaturation. Specific examples include: trimethylsiloxy-endblockeddimethylsiloxane-methylhexenylsiloxane copolymers;dimethylhexenylsiloxy-endblocked dimethylsiloxane-methylhexenylsiloxanecopolymers; trimethylsiloxy-endblockeddimethylsiloxane-methylvinylsiloxane copolymers;trimethylsiloxyl-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinysiloxane copolymers;dimethylvinylsiloxy-endblocked dimethylpolysiloxanes;dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxanecopolymers; dimethylvinylsiloxy-endblocked methylphenylpolysiloxanes;dimethylvinylsiloxy-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers;and the copolymers listed above wherein at least one group isdimethylhydroxysiloxy. Examples of commercially-available siliconessuitable for blending with compositions disclosed herein includeSILASTIC®. silicone rubber from Dow Corning Corporation of Midland,Mich.; BLENSIL® silicone rubber from GE of Waterford, N.Y.; andELASTOSIL® silicones from Wacker Chemie AG of Germany.

Other types of copolymers can also be added to the golf ballcompositions disclosed herein. For example, suitable copolymerscomprising epoxy monomers include styrene-butadiene-styrene blockcopolymers in which the polybutadiene block contains an epoxy group, andstyrene-isoprene-styrene block copolymers in which the polyisopreneblock contains epoxy. Examples of commercially-available epoxyfunctionalized copolymers include ESBS A1005, ESBS A1010, ESBS A1020,ESBS AT018, and ESBS AT019 epoxidized styrene-butadiene-styrene blockcopolymers from Daicel Chemical Industries of Japan.

Ionomeric compositions used to form golf ball layers of the presentinvention can be blended with non-ionic thermoplastic resins,particularly to manipulate product properties. Examples of suitablenon-ionic thermoplastic resins include, but are not limited to,polyurethane, poly-ether-ester, poly-amide-ether, polyether-urea, PEBAX®thermoplastic polyether block amides from Arkema Inc.,styrene-butadiene-styrene block copolymers,styrene(ethylene-butylene)-styrene block copolymers, polyamides,polyesters, polyolefins (e.g., polyethylene, polypropylene,ethylene-propylene copolymers, ethylene-(meth)acrylate,ethylene-(meth)acrylic acid, functionalized polymers with maleicanhydride grafting, epoxidation, etc., elastomers (e.g., EPDM,metallocene-catalyzed polyethylene) and ground powders of the thermosetelastomers.

Compositions disclosed herein can be either foamed or filled withdensity adjusting materials to provide desirable golf ball performancecharacteristics.

The present invention is limited to elevated temperature molding due tothe very-low-flow nature of the thermoplastic intermediate core layers.It should be understood that while any of the other core and/or coverlayer(s) can be formed by any suitable technique, including injectionmolding, compression molding, casting, and reaction injection molding,the thermoplastic inner cover layers are generally formed by injectionmolding or compression molding. In particular, the core center and outercore layers may be formed by any conventional means for formingthermosetting layers comprising a vulcanized or otherwise crosslinkeddiene rubber including, but not limited to, compression molding,rubber-injection molding, casting of a liquid rubber, and laminating.

When the thermoplastic inner cover layers are formed with injectionmolding, the composition is typically in a pelletized or granulated formthat can be fed into the throat of an injection molding machine where itis melted and conveyed via a screw in a heated barrel at temperatures offrom 400° F. (204° C.) to 680° F. (360° C.), preferably from 520° F.(271° C.) to 650° F. (343° C.). The molding temperatures aresignificantly higher temperatures than typically used for conventionalinjection molding of ionomeric materials.

The molten composition is ultimately injected into a closed mold cavity,which may be cooled, at ambient or at an elevated temperature, buttypically the mold is cooled to a temperature of from 50° F. (10° C.) to70° F. (21° C.). After residing in the closed mold for a time of about 1to 300 seconds, preferably about 20 to 120 seconds, the core and/or coreplus one or more additional core or cover layers is removed from themold and either allowed to cool at ambient or reduced temperatures or isplaced in a cooling fluid such as water, ice water, dry ice in asolvent, or the like.

When compression molding is used to form a core center or outer corelayer, the composition is first formed into a preform or slug ofmaterial, typically cylindrically-shaped or roughly spherical-shaped, ata weight slightly greater than the desired weight. Prior to this step,the composition may be first extruded or otherwise melted and forcedthrough a die after which it is cut into the preform. The preform isthen placed into a compression mold cavity and compressed at a moldtemperature of from 150° F. (66° C.) to 400° F. (204° C.), preferablyfrom 250° F. (121° C.) to 400° F. (204° C.), and more preferably from300° F. (149° C.) to 400° F. (204° C.). When compression molding a coverlayer, half-shells of the cover layer material are first formed viainjection molding. A core is then enclosed within two half-shells, whichis then placed into a compression mold cavity and compressed.

Reaction injection molding processes are further disclosed, for example,in U.S. Pat. Nos. 6,083,119, 7,208,562, 7,281,997, 7,282,169, and7,338,391, the entire disclosures of which are hereby incorporatedherein by reference.

Golf balls of the present invention typically have a coefficient ofrestitution of 0.700 or greater, preferably 0.750 or greater, and morepreferably 0.780 or greater. Golf balls of the present inventiontypically have a compression of 40 or greater, or a compression within arange having a lower limit of 50 or 60 and an upper limit of 100 or 120.Golf balls of the present invention will typically have dimple coverageof 60% or greater, preferably 65% or greater, and more preferably 75% orgreater.

The USGA specifications limit the minimum size of a competition golfball to 1.68 inches. There is no specification as to the maximumdiameter and golf balls of any size can be used for recreational play.Golf balls of the present invention can have an outer diameter of anysize. The preferred outer diameter is within a range having a lowerlimit of 1.680 inches and an upper limit of 1.740 or 1.760 or 1.780 or1.800 inches.

Golf balls of the present invention preferably have a moment of inertia(“MOI”) of about 70 to 95 gcm², preferably about 75 to 93 gcm², and morepreferably about 76 to 90 gcm². For low MOI embodiments, the golf ballpreferably has an MOI of 85 gcm² or less, or 83 gcm² or less. For highMOI embodiment, the golf ball preferably has an MOI of 86 gcm² orgreater, or 87 gcm² or greater. MOI is measured on a model MOI-005-104Moment of Inertia Instrument manufactured by Inertia Dynamics ofCollinsville, Conn.

Compression is an important factor in golf ball design. For example, thecompression of the core can affect the ball's spin rate off the driverand the feel. As disclosed in “Compression by Any Other Name,” Scienceand Golf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) by J. Dalton, several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, “compression” refers to Atti compression and is measuredaccording to a known procedure, using an Atti compression test device,wherein a piston is used to compress a ball against a spring. The travelof the piston is fixed and the deflection of the spring is measured. Themeasurement of the deflection of the spring does not begin with itscontact with the ball; rather, there is an offset of approximately thefirst 1.25 mm (0.05 inches) of the spring's deflection. Very lowstiffness cores will not cause the spring to deflect by more than 1.25mm and therefore have a zero compression measurement. The Atticompression tester is designed to measure objects having a diameter of1.680 inches; thus, smaller objects, such as golf ball cores, must beshimmed to a total height of 1.680 inches to obtain an accurate reading.Conversion from Atti compression to Riehle (cores), Riehle (balls), 100kg deflection, 130-10 kg deflection or effective modulus can be carriedout according to the formulas given in the Dalton article.

COR, as used herein, is determined according to a procedure where a golfball or golf ball subassembly (e.g., a core) is fired from an air cannonat two given velocities and calculated at a velocity of 125 ft/s.Ballistic light screens are located between the air cannon and the steelplate at a fixed distance to measure ball velocity. As the ball travelstoward the steel plate, it activates each light screen, and the time ateach light screen is measured. This provides an incoming transit timeperiod inversely proportional to the ball's incoming velocity. The ballimpacts the steel plate and rebounds though the light screens, whichagain measure the time period required to transit between the lightscreens. This provides an outgoing transit time period inverselyproportional to the ball's outgoing velocity. COR is then calculated asthe ratio of the outgoing transit time period to the incoming transittime period, COR=V(out)/V(in)=T(in)/T(out).

The surface hardness of a golf ball layer is obtained from the averageof a number of measurements taken from opposing hemispheres, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface, care must betaken to insure that the golf ball or golf ball subassembly is centeredunder the durometer indentor before a surface hardness reading isobtained. A calibrated, digital durometer, capable of reading to 0.1hardness units is used for all hardness measurements and is set to takehardness readings at 1 second after the maximum reading is obtained. Thedigital durometer must be attached to, and its foot made parallel to,the base of an automatic stand. The weight on the durometer and attackrate conform to ASTM D-2240.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within .+−.0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located180.degree. apart, or 90.degree. apart, respectively, and then averaged.All hardness measurements performed on a plane passing through thegeometric center are performed while the core is still in the holder andwithout having disturbed its orientation, such that the test surface isconstantly parallel to the bottom of the holder, and thus also parallelto the properly aligned foot of the durometer. Hardness points shouldonly be measured once at any particular geometric location.

For purposes of the present disclosure, a hardness gradient of a centeris defined by hardness measurements made at the outer surface of thecenter and the center point of the core. “Negative” and “positive” referto the result of subtracting the hardness value at the innermost portionof the golf ball component from the hardness value at the outer surfaceof the component. For example, if the outer surface of a solid centerhas a lower hardness value than the center (i.e., the surface is softerthan the center), the hardness gradient will be deemed a “negative”gradient. In measuring the hardness gradient of a center, the centerhardness is first determined according to the procedure above forobtaining the center hardness of a core. Once the center of the core ismarked and the hardness thereof is determined, hardness measurements atany distance from the center of the core may be measured by drawing aline radially outward from the center mark, and measuring and markingthe distance from the center, typically in 2 mm increments. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder. The hardness difference from anypredetermined location on the core is calculated as the average surfacehardness minus the hardness at the appropriate reference point, e.g., atthe center of the core for a single, solid core, such that a coresurface softer than its center will have a negative hardness gradient.

Hardness gradients are disclosed more fully, for example, in U.S. Pat.No. 7,429,221, and U.S. patent application Ser. Nos. 11/939,632;11/939,634; 11/939,635; and Ser. No. 11/939,637; the entire disclosureof each are hereby incorporated herein by reference.

It should be understood that there is a fundamental difference between“material hardness” and “hardness as measured directly on a golf ball.”For purposes of the present disclosure, material hardness is measuredaccording to ASTM D2240 and generally involves measuring the hardness ofa flat “slab” or “button” formed of the material. Hardness as measureddirectly on a golf ball (or other spherical surface) typically resultsin a different hardness value. This difference in hardness values is dueto several factors including, but not limited to, ball construction(i.e., core type, number of core and/or cover layers, etc.), ball (orsphere) diameter, and the material composition of adjacent layers. Itshould also be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other.

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused. All patents, publications, test procedures, and other referencescited herein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by those ofordinary skill in the art without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the examples and descriptions setforth herein, but rather that the claims be construed as encompassingall of the features of patentable novelty which reside in the presentinvention, including all features which would be treated as equivalentsthereof by those of ordinary skill in the art to which the inventionpertains.

What is claimed is:
 1. A golf ball comprising: a core; an inner coverlayer comprising a first thermoplastic composition and having athickness of about 0.005 inches to about 0.40 inches and a surfacehardness of about 60 Shore D or greater; and an outer cover layercomprising a thermoplastic polyurethane and having a thickness of about0.01 inches to about 0.075 inches and a surface hardness of about 60Shore D or less; wherein the first thermoplastic composition comprises afirst melt flow index at 280° C. under a 10-kg load of less than about35 g/10 min and a second melt flow index at 265° C. under a 5-kg load ofless than about 10 g/10 min.
 2. The golf ball of claim 1, wherein thefirst melt flow index is about 20 g/10 min or less.
 3. The golf ball ofclaim 2, wherein the first melt flow index is about 10 g/10 min or less.4. The golf ball of claim 3, wherein the second melt flow index is about5 g/10 min or less.
 5. The golf ball of claim 1, wherein the firstthermoplastic composition has a third melt flow index at 190° C. under a2.16-kg load of less than about 2 g/10 min.
 6. The golf ball of claim 5,wherein the third melt flow index is less than about 1 g/10 min.
 7. Thegolf ball of claim 1, wherein the first thermoplastic compositioncomprises an ionomer.
 8. The golf ball of claim 7, wherein the firstthermoplastic composition comprises a higher-melting-temperaturethermoplastic resin.
 9. The golf ball of claim 7, wherein the firstthermoplastic composition comprises a reactive polymer.
 10. The golfball of claim 7, wherein the ionomer is neutralized by a metal cation to80 wt % or greater.
 11. The golf ball of claim 10, wherein the ionomeris neutralized by a metal cation to 90 wt % or greater.
 12. The golfball of claim 1, wherein the first thermoplastic composition comprisesan amine or a peroxide compound.
 13. The golf ball of claim 1, whereinthe core comprises an inner core and an outer core layer.